Millimeter to Ri (Japanese) Converter
Convert millimeters to ri with our free online length converter.
Quick Answer
1 Millimeter = 2.546473e-7 ri
Formula: Millimeter × conversion factor = Ri (Japanese)
Use the calculator below for instant, accurate conversions.
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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.
Millimeter to Ri (Japanese) Calculator
How to Use the Millimeter to Ri (Japanese) Calculator:
- Enter the value you want to convert in the 'From' field (Millimeter).
- The converted value in Ri (Japanese) 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 Ri (Japanese): Step-by-Step Guide
Converting Millimeter to Ri (Japanese) involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Millimeter = 2.5465e-7 riExample Calculation:
Convert 10 millimeters: 10 × 2.5465e-7 = 2.5465e-6 ri
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.
Need to convert to other length units?
View all Length conversions →What is a Millimeter and a Ri (Japanese)?
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
The Ri (里) is a traditional Japanese unit of long distance, belonging to the Shakkanhō (尺貫法) system. It is defined as being equal to 36 chō (町).
Based on the standardized chō (which is 60 ken, with 1 ken = 6 shaku, and 1 shaku = 10/33 meters), the modern standardized Ri is equivalent to:
- 36 chō = 36 * (60 ken) = 36 * 60 * (6 shaku) = 12,960 shaku
- 12,960 * (10/33) meters = 129,600 / 33 meters = 43,200 / 11 meters
- Exactly 3927.2727... meters
- Approximately 3.927 kilometers (km)
- Approximately 2.440 miles (mi)
Historically, the Ri represented a significant travel distance, often conceptualized as roughly the distance a person could walk in one hour.
Note: The Millimeter is part of the metric (SI) system, primarily used globally in science and trade. The Ri (Japanese) belongs to the imperial/US customary system.
History of the Millimeter and Ri (Japanese)
-
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.
- Origin: The Japanese Ri unit, like many elements of the Shakkanhō measuring system, originates from ancient China, where the equivalent unit is the Li (里). This traditional unit of distance was adopted into Japan centuries ago.
- Variable Length: For much of Japanese history, the precise length of the Ri was not consistently fixed. Its value varied significantly depending on the region, the era, and even the specific context (e.g., measuring distance on flat land versus mountainous terrain). Different feudal domains (han) might use slightly different standards. For instance, during the Edo period (1603–1868), while a standard of 36 chō per Ri was common, local variations persisted, making historical distance conversions complex.
- Standardization (Meiji Era): Following the Meiji Restoration, Japan undertook efforts to modernize and standardize its systems, including weights and measures. The Weights and Measures Act of 1891 officially defined traditional Japanese units in relation to metric standards. The base unit shaku was set at 10/33 meters, which in turn fixed the values of the ken, chō, and consequently the Ri. The Ri was officially standardized as 36 chō, leading to the modern, precise value of 43,200/11 meters (approximately 3.93 km).
- Metrication: Japan officially adopted the metric system in 1951, with full implementation for official and commercial transactions mandated in 1959. This shift means the Ri became largely obsolete for practical, everyday measurements, replaced by the kilometer.
Common Uses and Applications: millimeters vs ri
Explore the typical applications for both Millimeter (metric) and Ri (Japanese) (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 ri
While the kilometer (km) is the standard unit for measuring long distances in modern Japan, the traditional Ri unit retains significance in specific contexts:
- Historical Context: Understanding the Ri is essential for interpreting historical travel accounts, old maps (like those showing the Tōkaidō road), and administrative divisions from feudal Japan. Landmarks called ichirizuka (一里塚 - "one-ri mound") were placed along major highways during the Edo period to mark distances in Ri.
- Literature and Culture: The Ri appears frequently in classical Japanese literature, poetry (like haiku), and folklore, often used to denote long journeys or significant, sometimes metaphorical, distances.
- Place Names: Many place names across Japan incorporate "Ri," often stemming from historical distance markers or locations whose names indicated their distance in Ri from a provincial capital or castle.
- Idioms and Proverbs: The unit features in well-known sayings, such as 「千里の道も一歩から」 (Sen ri no michi mo ippo kara - "A journey of a thousand ri begins with a single step"), emphasizing that even great undertakings start with small actions.
- Figurative Language: Speakers might use Ri figuratively to imply a very long way, a great effort, or a significant difference.
It is crucial to remember that the Ri is not used for contemporary official measurements, modern road signs (which universally use kilometers), or everyday distance calculations in Japan today.
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 Ri (Japanese) (ri)
How long is one Ri in meters or kilometers?
The modern standardized Japanese Ri is defined as 36 chō. This precise length equates to:
- Exactly 43,200 / 11 meters
- Approximately 3927.27 meters
- Approximately 3.927 kilometers (km)
- Approximately 2.440 miles (mi)
- Exactly 12,960 shaku (traditional Japanese feet)
Remember that historical values of the Ri could differ significantly before standardization.
How does the Ri relate to other traditional Japanese length units?
The Ri sits at the top of a hierarchy of length units in the traditional Shakkanhō system:
- 1 Ri = 36 chō (町)
- 1 chō = 60 ken (間)
- 1 ken = 6 shaku (尺)
- 1 shaku = 10 sun (寸)
Understanding these relationships is key to converting historical measurements.
Is the Japanese Ri the same length as the Chinese Li or Korean Ri?
No, although they share the same origin and written character (里), their standardized lengths differ significantly. It is important not to confuse them:
- Japanese Ri (modern): Approximately 3927 meters
- Chinese Li (modern): Exactly 500 meters (defined for compatibility with the metric system)
- Korean Ri (modern): Approximately 393 meters (standardized differently based on the Korean cheok)
Historical values for all three units also varied greatly over time and by region.
Is the Ri an SI unit?
No, the Ri is not part of the International System of Units (SI). It is a traditional Japanese unit belonging to the historical Shakkanhō system. The official SI base unit for length is the meter (m), and the derived unit commonly used for long distances globally is the kilometer (km).
Is the Ri unit still used today in Japan?
The Ri is very rarely used for practical measurement in modern Japan. Its usage is almost entirely confined to:
- Historical contexts (studying Japanese history, interpreting old maps, etc.)
- Cultural references (found in classic literature, proverbs, traditional idioms)
- Geographical place names
- Figurative language (to express long distances metaphorically)
For all official, commercial, and everyday distance measurements, the kilometer (km) is the standard unit used in Japan.
Conversion Table: Millimeter to Ri (Japanese)
| Millimeter (mm) | Ri (Japanese) (ri) |
|---|---|
| 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 |
People Also Ask
How do I convert Millimeter to Ri (Japanese)?
To convert Millimeter to Ri (Japanese), 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.
Learn more →What is the conversion factor from Millimeter to Ri (Japanese)?
The conversion factor depends on the specific relationship between Millimeter and Ri (Japanese). 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 Ri (Japanese) back to Millimeter?
Yes! You can easily convert Ri (Japanese) back to Millimeter by using the swap button (⇌) in the calculator above, or by visiting our Ri (Japanese) to Millimeter converter page. You can also explore other length conversions on our category page.
Learn more →What are common uses for Millimeter and Ri (Japanese)?
Millimeter and Ri (Japanese) 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.
Helpful Conversion Guides
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📚 How to Convert Units
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🔢 Conversion Formulas
Essential formulas for length and other conversions.
⚖️ Metric vs Imperial
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⚠️ Common Mistakes
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All Length Conversions
Other Length Units and Conversions
Explore other length units and their conversion options:
- Meter (m) • Millimeter to Meter
- Kilometer (km) • Millimeter to Kilometer
- Hectometer (hm) • Millimeter to Hectometer
- Decimeter (dm) • Millimeter to Decimeter
- Centimeter (cm) • Millimeter to Centimeter
- Inch (in) • Millimeter to Inch
- Foot (ft) • Millimeter to Foot
- Yard (yd) • Millimeter to Yard
- Mile (mi) • Millimeter to Mile
- Nautical Mile (NM) • Millimeter to Nautical Mile
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official US standards for length measurements
Bureau International des Poids et Mesures — International System of Units official documentation
Last verified: February 19, 2026