Millimeter to Parsec Converter

Convert millimeters to parsecs with our free online length converter.

Quick Answer

1 Millimeter = 3.240756e-20 parsecs

Formula: Millimeter × conversion factor = Parsec

Use the calculator below for instant, accurate conversions.

Our Accuracy Guarantee

All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.

Last verified: February 2026|Reviewed by: Sam Mathew, Software Engineer

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How to Use the Millimeter to Parsec Calculator:

Enter the value you want to convert in the 'From' field (Millimeter).
The converted value in Parsec will appear automatically in the 'To' field.
Use the dropdown menus to select different units within the Length category.
Click the swap button (⇌) to reverse the conversion direction.

How to Convert Millimeter to Parsec: Step-by-Step Guide

Converting Millimeter to Parsec involves multiplying the value by a specific conversion factor, as shown in the formula below.

Formula:

1 Millimeter = 3.2408e-20 parsecs

Example Calculation:

Convert 10 millimeters: 10 × 3.2408e-20 = 3.2408e-19 parsecs

Disclaimer: For Reference Only

These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.

Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.

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What is a Millimeter and a Parsec?

The millimeter (symbol: mm) is a unit of length in the metric system equal to one-thousandth of a meter (1/1,000 m) or one-tenth of a centimeter (1/10 cm). It is used for precise measurements in engineering, manufacturing, and everyday applications.

Key relationships:

1 millimeter = 0.001 meters (m)
1 millimeter = 0.1 centimeters (cm)
10 millimeters = 1 centimeter
1,000 millimeters = 1 meter
1 millimeter ≈ 0.03937 inches (about 1/25th inch)
25.4 millimeters = 1 inch (exactly)

The prefix "milli-":

From Latin "mille" meaning "thousand"
SI prefix denoting 10⁻³ (one-thousandth)
Also used in: milligram (mg), milliliter (mL), millisecond (ms)

Visual perspective (how big is it?):

1 mm = Thickness of a credit card
2 mm = Thickness of a US dime
5 mm = Thickness of a pencil lead (mechanical)
10 mm = Width of an adult fingernail
25.4 mm = Exactly one inch

Convert between length units: mm converter

and Standards

Geometric Definition

The parsec is defined through trigonometric parallax:

1 parsec = the distance at which 1 astronomical unit (AU) subtends an angle of 1 arcsecond (1″)

Mathematically:

1 parsec = 1 AU / tan(1″)
Since 1″ = 1/3600 degree = π/648,000 radians ≈ 4.8481 × 10⁻⁶ radians
For small angles: tan(θ) ≈ θ (in radians)
1 parsec ≈ 1 AU / 4.8481 × 10⁻⁶ ≈ 206,265 AU

Exact IAU Value

The International Astronomical Union (IAU) defines the parsec exactly as:

1 parsec = 648,000/π AU ≈ 206,264.806247 AU

Using the IAU-defined astronomical unit (1 AU = 149,597,870,700 meters exactly as of 2012):

1 parsec = 30,856,775,814,913,673 meters (exactly)

Or approximately:

3.0857 × 10¹⁶ meters
30.857 trillion kilometers
19.174 trillion miles

Relationship to Light-Year

The light-year (distance light travels in one Julian year) relates to the parsec:

1 parsec ≈ 3.26156 light-years

More precisely: 1 pc = 3.261563777 ly (using Julian year of 365.25 days)

Standard Multiples

Kiloparsec (kpc): 1 kpc = 1,000 pc ≈ 3,262 ly

Used for distances within galaxies
Milky Way diameter: ~30 kpc

Megaparsec (Mpc): 1 Mpc = 1,000,000 pc ≈ 3.26 million ly

Used for intergalactic distances
Andromeda Galaxy: ~0.77 Mpc

Gigaparsec (Gpc): 1 Gpc = 1,000,000,000 pc ≈ 3.26 billion ly

Used for cosmological distances
Observable universe radius: ~14 Gpc

Note: The Millimeter is part of the metric (SI) system, primarily used globally in science and trade. The Parsec belongs to the imperial/US customary system.

History of the Millimeter and Parsec

Metric System Origins: The millimeter was defined as a subunit of the meter when the metric system was established in France during the late 18th century (1790s). As measurement standardization progressed, the need for decimal subdivisions of the meter became clear.
Industrial Revolution: The millimeter became essential during the 19th century Industrial Revolution as:
- Precision machining required fine tolerances
- Interchangeable parts manufacturing emerged
- Engineering drawings needed standard units
- Technical specifications became international
Engineering Adoption: By the mid-19th century, engineers and machinists worldwide adopted millimeters as the standard for:
- Machine tool specifications
- Tolerance requirements (±0.1 mm common)
- Technical drawing dimensions
- Quality control measurements
Scientific Standardization: The millimeter became standard in scientific research for:
- Laboratory equipment calibration
- Microscopy measurements
- Specimen documentation
- Experimental apparatus dimensions
SI Formalization: When the International System of Units (SI) was established in 1960, the millimeter was confirmed as an official subdivision of the meter, forming part of the coherent decimal system.
Modern Manufacturing: The 20th century saw millimeters become universal in:
- Automotive engineering specifications
- Electronics manufacturing (PCB design)
- Aerospace tolerances
- Medical device specifications
- Consumer product dimensions
Global Standard: Today, millimeters are the primary unit for precision measurements in virtually every country except the United States (which uses both mm and inches). Even in the US, many technical fields have adopted millimeters as standard.

and Evolution

Pre-Parsec Era: The Parallax Quest (1600s-1830s)

The concept of stellar parallax dates to ancient Greek astronomy, but detecting it required centuries of technological advancement.

Galileo Galilei (1610) suggested that if Earth orbits the Sun, nearby stars should show annual parallax shifts against distant background stars. No parallax was detected, leading geocentrists to argue Earth must be stationary.

James Bradley (1728) discovered stellar aberration (apparent star position shifts due to Earth's orbital motion combined with finite light speed), confirming Earth's motion but still failing to detect parallax—stars were simply too distant.

Friedrich Wilhelm Bessel achieved the first successful parallax measurement in 1838 for 61 Cygni, determining a distance of about 10.3 light-years (3.16 parsecs, though the term didn't exist yet). This triumph came using a heliometer—a split-lens telescope enabling precise angular measurements.

Thomas Henderson measured Alpha Centauri's parallax (1832-1833, published 1839), and Friedrich Struve measured Vega's (1837), establishing parallax as the fundamental distance measurement method.

Coining the Term (1913)

Herbert Hall Turner (1861-1930), British astronomer and director of Oxford University Observatory, coined "parsec" in 1913. Before this, astronomers expressed stellar distances awkwardly:

In astronomical units (requiring numbers in the hundreds of thousands)
In light-years (popular but not directly tied to measurement method)
In "parallax seconds" (inverse of parallax angle, but confusing terminology)

Turner recognized that astronomers naturally thought in terms of parallax angles. For a star with parallax angle p (in arcseconds), the distance d is simply:

d (in parsecs) = 1 / p (in arcseconds)

This elegant relationship made the parsec immediately practical. A star with 0.5″ parallax is 2 parsecs away; 0.1″ parallax means 10 parsecs; 0.01″ parallax means 100 parsecs.

IAU Adoption (1922-1938)

The 1922 IAU General Assembly in Rome endorsed the parsec as the standard unit for stellar distances, though adoption wasn't immediate or universal.

The 1938 IAU General Assembly in Stockholm formally standardized the parsec definition based on the astronomical unit and arcsecond, solidifying its status.

By the 1950s, the parsec dominated professional astronomy literature, though popular science continued preferring light-years for general audiences.

Space Age Precision (1960s-Present)

Hipparcos satellite (1989-1993): European Space Agency mission measured parallaxes for 118,000 stars with milliarcsecond precision, extending reliable parsec-based distances to hundreds of parsecs.

Gaia mission (2013-present): ESA's Gaia spacecraft has revolutionized astrometry, measuring parallaxes for 1.8 billion stars with microarcsecond precision. This extends direct parsec measurements to 10,000+ parsecs (10+ kiloparsecs), mapping our galaxy's structure in unprecedented detail.

2012 IAU redefinition: The IAU redefined the astronomical unit as exactly 149,597,870,700 meters (no longer based on Earth's actual orbit, which varies slightly). This made the parsec exactly 648,000/π AU, providing a stable definition independent of Earth's orbital variations.

Common Uses and Applications: millimeters vs parsecs

Explore the typical applications for both Millimeter (metric) and Parsec (imperial/US) to understand their common contexts.

Common Uses for millimeters

The millimeter is the standard unit for precise measurements across multiple fields:

Engineering & Machining

Precise measurement requirements for manufacturing, quality control, and technical specifications. Essential for maintaining tolerances in mechanical parts.

Why millimeters in engineering:

Decimal system (easy calculations)
International standard (ISO)
Suitable precision range
Compatible with CNC machinery
Standard drawing units

Applications:

Machine tool specifications
Part tolerances (±0.05 mm common)
Technical drawing dimensions
CAD/CAM software units
Quality inspection reports

Convert for technical work: mm to inches | mm to cm

Technical Design & Drafting

Standard measurement unit for architectural, mechanical, and technical drawings worldwide.

Drawing Standards:

ISO standards use millimeters
Engineering drawings in mm
Architecture plans (many countries)
Product design specifications
Patent drawings (international)

Why mm for drawings:

Eliminates fractions (unlike inches)
Scales easily (1:10, 1:100, etc.)
International communication
CAD software standard

Electronics & PCB Design

Measuring component sizes, trace widths, and circuit board dimensions in electronic manufacturing.

PCB Design:

Trace width: 0.25-1 mm
Component footprints: mm specifications
Hole diameters: 0.6-1.2 mm
Board thickness: 1.6 mm standard
Component spacing: mm grid

Component Specs:

All modern ICs specified in mm
Resistor/capacitor sizes (mm codes)
Connector dimensions
Display module sizes

Meteorology & Climate

Measuring rainfall amounts with precision, essential for weather forecasting, agriculture, and climate research.

Rain Gauges:

Standard measurement unit worldwide
Collected in graduated cylinders (mm scale)
Automated weather stations use mm
Historical records in mm
Climate data standardized

Importance:

Drought assessment
Flood prediction
Agricultural planning
Water resource management
Climate change tracking

Use our mm converter for scientific calculations.

Manufacturing & Quality Control

Inspecting product dimensions and ensuring parts meet specifications within required tolerances.

QC Measurements:

Caliper readings in mm
Micrometer measurements
Coordinate measuring machines (CMM)
Surface profile measurements
Dimensional inspection reports

Industries:

Automotive parts
Aerospace components
Medical devices
Consumer electronics
Precision instruments

Jewelry & Watchmaking

Specifying sizes of gems, watch cases, and jewelry components with precision.

Why jewelers use mm:

International gem standard
Precise size communication
Watch industry standard
Setting specifications
Customer communication

Measurements:

Gemstone dimensions
Ring widths and thicknesses
Watch case diameters
Bracelet link sizes
Clasp dimensions

Medical Measurements

Documenting precise measurements in diagnostics, surgery planning, and treatment monitoring.

Clinical Uses:

Imaging measurements (CT, MRI, X-ray)
Tumor size tracking
Surgical planning
Needle specifications
Medical device dimensions

Why mm in medicine:

International standard
Appropriate precision
Imaging system default
Research compatibility
Treatment standardization

When to Use parsecs

Stellar Astronomy and Parallax Measurements

The parsec's primary use is measuring stellar distances via trigonometric parallax:

Parallax formula: d (parsecs) = 1 / p (arcseconds)

Ground-based observatories: Measure parallaxes to ~0.01″ accuracy, reliable to ~100 pc

Hipparcos satellite: Measured parallaxes to ~0.001″ (1 milliarcsecond), reliable to ~1,000 pc (1 kpc)

Gaia spacecraft: Measures parallaxes to ~0.00001″ (10 microarcseconds) for bright stars, reliable to ~10 kpc for many stars

Applications:

Calibrating the cosmic distance ladder (using Cepheid variables, RR Lyrae stars)
Determining absolute magnitudes of stars
Studying stellar populations and galactic structure
Measuring proper motions and space velocities

Galactic Structure and Dynamics

Kiloparsecs (kpc) describe structures within galaxies:

Milky Way structure:

Galactic center (Sagittarius A*): 8.2 kpc from Sun
Galactic disk radius: ~15 kpc
Central bulge: ~1.5 kpc radius
Spiral arms: trace patterns 10-15 kpc in radius
Dark matter halo: extends to ~60 kpc

Rotation curves: Plot orbital velocity vs. distance (in kpc) from galactic center, revealing dark matter

Star formation regions: Giant molecular clouds span 10-100 pc

Globular clusters: Orbit 10-60 kpc from galactic center

Extragalactic Astronomy

Megaparsecs (Mpc) measure distances between galaxies:

Galaxy surveys: Map millions of galaxies to distances of 1,000+ Mpc, revealing large-scale structure (walls, filaments, voids)

Tully-Fisher relation: Links galaxy rotation speed to luminosity, enabling distance estimates in Mpc

Type Ia supernovae: Standard candles for measuring distances to 1,000+ Mpc

Galaxy clusters: Typical separation between major clusters ~10-50 Mpc

Superclusters: Structures spanning 100-200 Mpc (like Laniakea Supercluster containing Milky Way)

Cosmology and Universe Expansion

Megaparsecs and gigaparsecs describe cosmological distances:

Hubble constant (H₀): Measured in km/s per Mpc—describes universe expansion rate

Current value: H₀ ≈ 67-73 (km/s)/Mpc (tension between measurement methods)
Interpretation: Galaxy 1 Mpc away recedes at ~70 km/s; 100 Mpc away recedes at ~7,000 km/s

Hubble's Law: v = H₀ × d (where d is in Mpc, v is recession velocity)

Comoving distance: Cosmological distance accounting for universe expansion, measured in Mpc or Gpc

Redshift surveys: Map galaxy distribution to 1,000+ Mpc (z ~ 0.1-0.3 redshift)

Baryon acoustic oscillations: ~150 Mpc characteristic scale in galaxy distribution, used as "standard ruler"

Astrophysical Research Papers

Parsecs are the default distance unit in professional astronomy journals:

Observational papers: Report star/galaxy distances in pc, kpc, or Mpc

Theoretical models: Express scale lengths in parsecs (e.g., "disk scale length of 3 kpc")

Computer simulations: Use parsec-based units (or comoving kpc/Mpc for cosmological sims)

Standard convention: Professional astronomers think and calculate in parsecs, converting to light-years only for public communication

Additional Unit Information

About Millimeter (mm)

How many millimeters are in a centimeter?

There are exactly 10 millimeters (mm) in 1 centimeter (cm).

Conversion:

1 cm = 10 mm
To convert cm to mm: multiply by 10
To convert mm to cm: divide by 10

Examples:

5 cm = 50 mm
2.5 cm = 25 mm
75 mm = 7.5 cm

Memory aid: "Centi-" means 1/100 meter, "milli-" means 1/1,000 meter, so 10 mm = 1 cm.

Use our cm to mm converter for instant conversions.

How many millimeters are in a meter?

There are exactly 1,000 millimeters (mm) in 1 meter (m).

Conversion:

1 m = 1,000 mm
To convert m to mm: multiply by 1,000
To convert mm to m: divide by 1,000

Examples:

0.5 m = 500 mm
1.5 m = 1,500 mm
2,750 mm = 2.75 m

Remember: "Milli-" means one-thousandth, so it takes 1,000 mm to make 1 meter.

Convert: mm to meters | meters to mm

What does 'milli' mean in millimeter?

The prefix 'milli-' denotes one-thousandth (1/1,000).

Meaning:

Comes from Latin "mille" meaning "thousand"
In metric system: milli- = 10⁻³ = 1/1,000
1 millimeter = 1/1,000 of a meter = 0.001 m

Other "milli-" units:

Milligram (mg) = 1/1,000 gram
Milliliter (mL) = 1/1,000 liter
Millisecond (ms) = 1/1,000 second
Milliamp (mA) = 1/1,000 ampere

Pattern: Always divide by 1,000 to get the base unit.

How thick is 1 millimeter?

1 millimeter is very thin - about the thickness of:

Common objects:

Credit card: 0.76 mm (slightly thinner)
US dime: 1.35 mm (slightly thicker)
10 sheets of paper: ~1 mm
Paperclip wire: ~1 mm diameter
Mechanical pencil lead (0.7mm): Slightly thinner

Visual comparison:

Thinner than a US penny (1.55 mm)
About 1/25th of an inch (0.04 inches)
10 millimeters = 1 cm = width of fingernail

To visualize: Look at the edge of a credit card - that's less than 1 mm.

How many mm in an inch?

1 inch = 25.4 millimeters exactly (by international agreement).

This is a defined conversion (not an approximation):

1 inch ≡ 25.4 mm (exact)
1 mm = 1/25.4 inch ≈ 0.03937 inches

Common conversions:

1 inch = 25.4 mm
2 inches = 50.8 mm
3 inches = 76.2 mm
4 inches = 101.6 mm
12 inches (1 foot) = 304.8 mm

Reverse examples:

10 mm ≈ 0.394 inches
25 mm ≈ 0.984 inches (almost 1 inch)
50 mm ≈ 1.969 inches (almost 2 inches)

Memory trick: 25 mm is almost 1 inch (close enough for quick estimates).

Use our inch to mm converter for precise conversions.

What is 10mm in real life?

10 millimeters = 1 centimeter - about the width of an adult fingernail.

Common 10mm objects:

Fingernail width (adult index finger)
AA battery diameter: 14 mm (close)
Small marble: ~10-15 mm diameter
M10 bolt diameter: 10 mm
Thick cardboard: ~10 mm

Comparisons:

Just under 0.4 inches (0.394 inches exactly)
Thickness of 100 sheets of paper
About 3/8 inch (slightly larger)

In measurements:

Camera/phone thickness: Often 7-10 mm
Watch case thickness: Often 10-12 mm
Pencil diameter: ~7-8 mm (10mm would be thick)

How do you read a metric ruler?

Metric rulers are divided into centimeters (cm) and millimeters (mm):

Reading steps:

Large numbers: Centimeters (0, 1, 2, 3...)
Long lines: Each centimeter mark
Short lines: Millimeters (10 per cm)
Count: From zero to your measurement point

Example reading:

Between 3 and 4 cm, at the 7th small line = 3.7 cm or 37 mm
At the 15th cm mark = 15 cm or 150 mm

Tips:

10 small marks = 1 cm
Each small mark = 1 mm
Halfway between cm marks = 5 mm
Read to nearest 0.5 mm for precision

Reporting:

Small objects: Use mm (e.g., "15 mm")
Larger objects: Use cm (e.g., "15.5 cm")
Both are correct, choose clearer one

What tools measure millimeters?

Many tools measure in millimeters:

Hand Tools:

Metric ruler: Basic measurement to 1 mm
Metric tape measure: Construction/carpentry
Caliper: Precision to 0.01 mm (digital/vernier)
Micrometer: Very precise, to 0.001 mm
Depth gauge: Measuring depths and heights

Digital Tools:

Digital caliper: Easy reading, 0.01 mm precision
Laser distance meter: Millimeter accuracy
Height gauge: Vertical measurements
Coordinate measuring machine (CMM): Industrial precision

Specialized Tools:

Feeler gauge: Thin strips in mm thicknesses
Thread gauge: Checking thread pitch (mm)
Bore gauge: Internal diameter measurement
Pin gauge: Precision hole measurement

Which to use:

Ruler: General purpose (±0.5 mm)
Caliper: Precision work (±0.01 mm)
Micrometer: Very tight tolerances (±0.001 mm)

Is mm smaller than cm?

Yes, millimeters (mm) are smaller than centimeters (cm).

Relationship:

1 cm = 10 mm
1 mm = 0.1 cm
Millimeter is 10 times smaller than centimeter

Scale comparison:

Largest: meter (m)
Middle: centimeter (cm) = 1/100 m
Smallest: millimeter (mm) = 1/1,000 m

Visual:

Width of fingernail: 1 cm = 10 mm
Thickness of dime: 1.35 mm (can't easily express in cm)

When to use each:

Use mm: Small, precise measurements (< 100 mm)
Use cm: Medium measurements (1-100 cm)
Use m: Large measurements (> 1 meter)

Example:

Pencil length: 19 cm or 190 mm (19 cm clearer)
Wire diameter: 2 mm (not 0.2 cm - awkward)

How much rain is 1mm?

1 millimeter of rain means 1 mm depth of water would cover a flat surface if none drained away.

What it means:

1 mm rain = 1 liter per square meter of water
Light drizzle might produce 1-2 mm/hour
Barely enough to wet the ground thoroughly

Rain intensity scale:

Trace-1 mm: Very light drizzle
1-2 mm: Light rain
2-5 mm: Light to moderate rain
5-10 mm: Moderate rain
10-20 mm: Heavy rain
20-50 mm: Very heavy rain
>50 mm: Extreme rainfall (per hour)

Practical impact:

1 mm: Barely wets surfaces
10 mm: Significant watering
25 mm: Heavy rain event
100 mm: Major storm (in 24 hours)

Measurement:

Rain gauge collects water
Depth measured in mm
Standard worldwide for weather reporting

About Parsec (pc)

What does "parsec" stand for?

Parsec is a portmanteau of "parallax of one arcsecond."

It represents the distance at which Earth's orbital radius (1 AU) subtends an angle of exactly one arcsecond (1/3600 of a degree). British astronomer Herbert Hall Turner coined the term in 1913 to provide a convenient unit directly tied to the parallax measurement method.

How is a parsec measured?

Parsecs are measured using trigonometric parallax:

Observe a nearby star from Earth when Earth is on one side of its orbit
Observe the same star six months later when Earth is on the opposite side
Measure the apparent shift in the star's position against distant background stars
Half this shift is the parallax angle p (in arcseconds)
Calculate distance: d = 1/p parsecs

Modern method: Space telescopes like Gaia measure parallax angles with microarcsecond precision, enabling distance measurements to thousands of parsecs.

Is a parsec bigger than a light-year?

Yes, one parsec is significantly larger:

1 parsec ≈ 3.26 light-years

More precisely: 1 pc = 3.261563777 ly

Example: Proxima Centauri at 1.3 parsecs equals 4.24 light-years away.

Why the difference matters: Confusing parsecs with light-years introduces 3× error in distances.

Why do astronomers prefer parsecs over light-years?

Astronomers prefer parsecs for several reasons:

1. Direct observational connection: Parallax angle p (arcseconds) directly gives distance d = 1/p (parsecs). No complicated conversion needed.

2. Professional standard: IAU endorsed parsecs in 1922; they're now universal in research papers and textbooks.

3. Convenient multiples: Kiloparsecs (kpc) for galactic distances, megaparsecs (Mpc) for cosmological distances provide natural scales.

4. Hubble constant units: Universe expansion rate naturally expressed in (km/s)/Mpc.

5. Definition stability: Light-year depends on year length definition (tropical, Julian, sidereal); parsec defined purely by geometry.

Light-years remain popular in public communication because "year" is familiar, while "parallax arcsecond" requires technical knowledge.

How many astronomical units are in a parsec?

1 parsec = 206,265 astronomical units (AU) (approximately)

More precisely: 1 pc = 206,264.806247 AU

This number arises from: 1 pc = 1 AU / tan(1″), and since 1″ = π/648,000 radians:

1 pc = 1 AU / (π/648,000) = 648,000/π AU ≈ 206,265 AU

Context: Since 1 AU ≈ 150 million km (Earth-Sun distance), 1 parsec ≈ 31 trillion km.

What is a kiloparsec and megaparsec?

Kiloparsec (kpc): 1 kpc = 1,000 parsecs ≈ 3,262 light-years

Used for: Galactic-scale distances
Examples: Sun to Milky Way center (8 kpc), galaxy diameters (10-50 kpc)

Megaparsec (Mpc): 1 Mpc = 1,000,000 parsecs ≈ 3.26 million light-years

Used for: Intergalactic distances, cosmology
Examples: Andromeda Galaxy (0.77 Mpc), Virgo Cluster (16.5 Mpc), Hubble constant measured in (km/s)/Mpc

Gigaparsec (Gpc): 1 Gpc = 1,000,000,000 parsecs ≈ 3.26 billion light-years

Used for: Large-scale cosmological structures
Example: Observable universe radius (~14 Gpc)

Is the parsec an SI unit?

No, the parsec is not an SI unit. The SI unit of length is the meter (m).

However, the parsec is:

Recognized by the IAU (International Astronomical Union)
Accepted for use with SI in astronomy contexts
Defined exactly in terms of the AU (which is defined exactly in meters)

Why not SI?: The parsec arose naturally from astronomical practice and remains far more practical than expressing stellar distances in meters (which would require numbers like 10¹⁶ to 10²³).

Analogy: Like the electronvolt (eV) in particle physics, the parsec is a specialized unit indispensable to its field despite not being SI.

How far can parallax measure distances?

Ground-based telescopes: ~0.01 arcsecond precision → reliable to ~100 parsecs

Hubble Space Telescope: ~0.001 arcsecond (1 milliarcsecond) → reliable to ~1,000 parsecs (1 kpc)

Hipparcos satellite (1989-1993): ~0.001 arcsecond → 118,000 stars measured to 100-1,000 pc

Gaia spacecraft (2013-present): ~0.00001 arcsecond (10 microarcseconds) for bright stars → reliable to ~10,000 parsecs (10 kpc)

Measured 1.8 billion stars
Revolutionary precision enables mapping entire Milky Way disk

Fundamental limit: Stars beyond 10-20 kpc have unmeasurably small parallaxes with current technology. For greater distances, astronomers use indirect methods (Cepheids, Type Ia supernovae, redshift).

Did Han Solo make the Kessel Run in "less than 12 parsecs"?

Famous Star Wars quote: "She made the Kessel Run in less than twelve parsecs."

The issue: Parsec measures distance, not time. Saying "less than 12 parsecs" for a speed achievement is like saying "I drove to work in less than 5 miles."

Fan explanations (retroactive justifications):

The Kessel Run involves navigating near black holes; a shorter distance means a more dangerous, direct route
Skilled pilots can shave distance by flying closer to gravitational hazards
This reinterprets "12 parsecs" as boasting about route optimization, not speed

Real answer: George Lucas likely confused parsecs with a time unit when writing the script. The line became famous enough that later writers invented explanations making it technically correct.

Takeaway: In real astronomy, parsecs always measure distance, never time.

How do parsecs relate to the Hubble constant?

The Hubble constant (H₀) describes universe expansion and is typically expressed as:

H₀ ≈ 70 (km/s)/Mpc

Interpretation: For every megaparsec of distance, recession velocity increases by ~70 km/s.

Examples using Hubble's Law (v = H₀ × d):

Galaxy 1 Mpc away: recedes at ~70 km/s
Galaxy 10 Mpc away: recedes at ~700 km/s
Galaxy 100 Mpc away: recedes at ~7,000 km/s
Galaxy 1,000 Mpc away: recedes at ~70,000 km/s

Hubble length: c/H₀ ≈ 4,400 Mpc (14.4 billion ly) - characteristic distance scale of observable universe

Why Mpc?: Using megaparsecs keeps Hubble constant values convenient (70 rather than 0.000000000070 if using parsecs, or 2.3 × 10⁻¹⁸ if using SI meters).

What's the farthest distance ever measured in parsecs?

Observable universe radius: ~14,000 Mpc = 14 Gpc (46 billion light-years comoving distance)

Most distant galaxy observed (as of 2023): JADES-GS-z13-0 at redshift z ≈ 13.2

Comoving distance: ~4,200 Mpc (13.7 billion light-years light-travel distance)
Due to universe expansion, it's now ~10,000 Mpc (32 billion light-years) away

Cosmic microwave background: Emitted 380,000 years after Big Bang

Comoving distance to CMB surface: ~14,000 Mpc (46 billion light-years)

Beyond measurement: The observable universe has a finite size (~14 Gpc radius) due to finite age and light speed. Objects beyond this "cosmological horizon" are unobservable because their light hasn't reached us yet.

Conversion Table: Millimeter to Parsec

Millimeter (mm)	Parsec (pc)
0.5	0
1	0
1.5	0
2	0
5	0
10	0
25	0
50	0
100	0
250	0
500	0
1,000	0

How do I convert Millimeter to Parsec?

To convert Millimeter to Parsec, enter the value in Millimeter in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our length converter page to convert between other units in this category.

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What is the conversion factor from Millimeter to Parsec?

The conversion factor depends on the specific relationship between Millimeter and Parsec. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.

Can I convert Parsec back to Millimeter?

Yes! You can easily convert Parsec back to Millimeter by using the swap button (⇌) in the calculator above, or by visiting our Parsec to Millimeter converter page. You can also explore other length conversions on our category page.

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What are common uses for Millimeter and Parsec?

Millimeter and Parsec are both standard units used in length measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our length converter for more conversion options.

For more length conversion questions, visit our FAQ page or explore our conversion guides.

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Meter to Kilometer Meter to Hectometer Meter to Decimeter Meter to Centimeter Meter to Millimeter Meter to Inch Meter to Foot Meter to Yard Meter to Mile Meter to Nautical Mile Meter to Micrometer Meter to Nanometer Meter to Light Year Meter to Astronomical Unit Meter to Parsec Meter to Angstrom Meter to Point (Typography)Meter to Mil/Thou Meter to Fathom Meter to Furlong Meter to Link (Gunter's)Meter to Pace Meter to Span Meter to Digit Meter to Cable Length Meter to Ell Meter to Finger Meter to Roman Mile Meter to Stadion Meter to Chi (Chinese)Meter to Shaku (Japanese)Meter to Li (Chinese)Meter to Toise Meter to Bolt Meter to Rope Meter to Smoot Meter to Sajene Meter to Ken Meter to Wa Meter to Vara Meter to Aln Meter to Cubit (Royal/Egyptian)Meter to Versta Meter to Arpent Meter to Ri (Japanese)Meter to Klafter Meter to Yojana Meter to Skein Kilometer to Meter Kilometer to Hectometer Kilometer to Decimeter Kilometer to Centimeter Kilometer to Millimeter Kilometer to Inch Kilometer to Foot Kilometer to Yard Kilometer to Mile Kilometer to Nautical Mile Kilometer to Micrometer Kilometer to Nanometer Kilometer to Light Year Kilometer to Astronomical Unit Kilometer to Parsec Kilometer to Angstrom Kilometer to Point (Typography)Kilometer to Mil/Thou Kilometer to Fathom Kilometer to Furlong Kilometer to Link (Gunter's)Kilometer to Pace Kilometer to Span Kilometer to Digit Kilometer to Cable Length Kilometer to Ell Kilometer to Finger Kilometer to Roman Mile Kilometer to Stadion Kilometer to Chi (Chinese)Kilometer to Shaku (Japanese)Kilometer to Li (Chinese)Kilometer to Toise Kilometer to Bolt Kilometer to Rope Kilometer to Smoot Kilometer to Sajene Kilometer to Ken Kilometer to Wa Kilometer to Vara Kilometer to Aln Kilometer to Cubit (Royal/Egyptian)Kilometer to Versta Kilometer to Arpent Kilometer to Ri (Japanese)Kilometer to Klafter Kilometer to Yojana Kilometer to Skein Hectometer to Meter Hectometer to Kilometer Hectometer to Decimeter Hectometer to Centimeter Hectometer to Millimeter Hectometer to Inch Hectometer to Foot Hectometer to Yard Hectometer to Mile Hectometer to Nautical Mile Hectometer to Micrometer Hectometer to Nanometer Hectometer to Light Year Hectometer to Astronomical Unit Hectometer to Parsec Hectometer to Angstrom Hectometer to Point (Typography)Hectometer to Mil/Thou Hectometer to Fathom Hectometer to Furlong Hectometer to Link (Gunter's)Hectometer to Pace Hectometer to Span Hectometer to Digit

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