Pascal (Pa) - Unit Information & Conversion

Quick Answer

What is a pascal? The pascal (Pa) is the SI unit of pressure equal to one newton per square meter (1 N/m²). It measures force distributed over an area, quantifying how much force presses on each square meter of surface. While atmospheric pressure at sea level equals 101,325 Pa (101.3 kPa), the pascal is very small for most applications—tire pressure is typically 200-250 kPa, while concrete strength is measured in megapascals (MPa). 1 pascal = 0.000145 PSI = 0.00001 bar = 0.001 kPa. Use our pressure converter for all your pascal conversions.

Quick Comparison Table

Pressure Unit	Equivalent to 1 Pascal	Common Uses
Pascal (Pa)	1 Pa	Sound pressure, vacuum, small differentials
Kilopascal (kPa)	0.001 kPa	Tire pressure, weather, HVAC, engineering
Megapascal (MPa)	0.000001 MPa	Material strength, hydraulics, high pressure
Bar	0.00001 bar	European industrial, scuba diving, turbines
PSI	0.000145 PSI	US/UK tire pressure, industrial equipment
Atmosphere (atm)	0.00000987 atm	Diving depths, gas storage, high-pressure processes
mmHg/Torr	0.0075 mmHg	Blood pressure, vacuum systems, medical
Hectopascal (hPa)	0.01 hPa	Meteorology (identical to millibar: 1 hPa = 1 mbar)

Real-world anchors: Sea-level atmospheric pressure = 101,325 Pa = 101.3 kPa = 1013 hPa = 1.013 bar = 14.7 PSI = 1 atm = 760 mmHg

Definition and Standards

The pascal is defined as:

Fundamental SI Definition

1 Pa = 1 N/m² (one newton per square meter)

In base SI units: 1 Pa = 1 kg/(m·s²)

This means one pascal represents a force of one newton distributed uniformly over one square meter of surface area.

Relationship to Force and Area

• Force: 1 N (newton) = the force needed to accelerate 1 kg at 1 m/s²
• Area: 1 m² = a square with 1-meter sides
• Pressure: 1 Pa = 1 N spread over 1 m² = very little pressure

Practical perspective: 1 Pa ≈ the pressure from a dollar bill (1 gram) resting flat on a table (spread over ~160 cm²).

Standard Conversions

• 1 kPa = 1,000 Pa (kilopascal)
• 1 MPa = 1,000,000 Pa = 1,000 kPa (megapascal)
• 1 GPa = 1,000,000,000 Pa = 1,000 MPa (gigapascal)
• 1 bar = 100,000 Pa = 100 kPa
• 1 atmosphere = 101,325 Pa = 101.325 kPa = 1.01325 bar
• 1 PSI = 6,894.76 Pa = 6.895 kPa
• 1 mmHg = 133.322 Pa (millimeter of mercury/Torr)
• 1 hectopascal (hPa) = 100 Pa = 1 millibar (mbar)

Why Pascal is "Too Small"

Most everyday pressures are thousands or millions of pascals:

• Human breath: ~1,000 Pa = 1 kPa
• Car tire: 220,000 Pa = 220 kPa = 32 PSI
• Atmospheric pressure: 101,325 Pa = 101.3 kPa
• Hydraulic jack: 10,000,000 Pa = 10 MPa = 1,450 PSI
• Concrete compressive strength: 30,000,000 Pa = 30 MPa

This is why kilopascals (kPa) and megapascals (MPa) dominate practical engineering and everyday use.

History and Evolution

Blaise Pascal (1623-1662)

Blaise Pascal, born in Clermont-Ferrand, France, was a mathematical prodigy who made revolutionary contributions to geometry, probability theory, and physics before his death at age 39. His work on fluid mechanics fundamentally changed scientific understanding of pressure and laid the groundwork for hydraulic engineering.

Early Work (1640s):

• At age 18, Pascal invented one of the first mechanical calculators (the Pascaline) to help his father with tax calculations
• Conducted experiments with barometers following Evangelista Torricelli's invention of the mercury barometer (1643)
• Investigated why mercury columns in barometers didn't rise beyond ~76 cm, hypothesizing atmospheric pressure as the cause

Puy de Dôme Experiment (1648): Pascal's brother-in-law Florin Périer carried a barometer to the top of Puy de Dôme mountain (1,465 m elevation) while Pascal monitored a barometer at the base. The mercury column dropped approximately 7.6 cm at the summit—conclusive proof that atmospheric pressure decreases with altitude. This experiment demolished the prevailing Aristotelian theory that "nature abhors a vacuum" and established that air has weight and creates pressure.

Pascal's Law (1653): Pascal formulated the principle that pressure applied to a confined incompressible fluid is transmitted undiminished throughout the fluid in all directions. This fundamental law enabled:

• Hydraulic presses (multiplying force)
• Hydraulic brakes (automotive, aircraft)
• Hydraulic jacks and lifts
• Modern fluid power systems

Pascal's Contributions to Pressure Science:

• Established that atmospheric pressure results from the weight of air above
• Demonstrated pressure-altitude relationships
• Developed theoretical foundations for hydrostatics
• Explained barometer operation mechanically rather than mystically

Development of Pressure Units (1600s-1900s)

Pre-metric era: Pressure was measured in bewildering variety:

• Inches/mm of mercury (inHg, mmHg): Based on barometer height
• Feet/meters of water: Hydraulic pressure measurement
• Pounds per square inch (PSI): English/American engineering
• Atmospheres (atm): Referenced to sea-level air pressure
• Technical atmospheres (at): 1 kgf/cm² (kilogram-force per square centimeter)

Metric standardization (1795-1960):

• Bar introduced 1909: 1 bar = 100,000 Pa = 0.9869 atm (almost 1 atmosphere)
• Widely used in European meteorology and engineering throughout 20th century
• Simple decimal relationship to atmosphere made it practical

SI Adoption (1960-1971):

• 1960: 11th CGPM established Système International d'Unités (SI)
• 1971: 14th CGPM officially adopted pascal as the SI unit of pressure
• Named to honor Blaise Pascal's foundational work 300+ years earlier
• Defined as 1 Pa = 1 N/m² = 1 kg/(m·s²)

Global Adoption Timeline

1970s-1980s: Scientific community adopted pascal as standard

• International standards organizations (ISO, IEC) specified pascal/kPa/MPa
• Scientific journals required SI units in publications
• Engineering textbooks transitioned to pascal-based examples

1990s-2000s: Industrial and commercial transition

• European Union metrication: tire pressures labeled in kPa
• Automotive specifications: engine pressures in kPa/MPa
• Meteorology: hectopascal (hPa) became standard for atmospheric pressure worldwide

Current Status (2020s):

• Universal in science: All research publications use pascals
• Global engineering: ISO standards, material specifications use Pa/kPa/MPa
• Weather reports: hectopascals (hPa) worldwide except US (uses inches Hg)
• Mixed usage: Tire pressure varies by region (kPa in most countries, PSI in US/UK)
• Holdouts: US aviation still uses inches Hg; blood pressure universally mmHg

Real-World Examples and Applications

Atmospheric and Weather Pressure

Standard Atmospheric Pressure (Sea Level):

• 101,325 Pa = 101.3 kPa = 1013 hPa = 1013.25 mbar
• Weather reports use hectopascals (hPa): "Pressure is 1015 hPa"
• 1 hPa = 100 Pa = 1 millibar (mbar)—meteorologists use these terms interchangeably

Weather Variations:

• High pressure system: 1020-1040 hPa (102-104 kPa) = clear, stable weather
• Low pressure system: 980-1000 hPa (98-100 kPa) = storms, precipitation
• Hurricane center: 900-950 hPa (90-95 kPa) = extreme low pressure
• Record low: 870 hPa (Typhoon Tip, 1979)—catastrophic storm
• Record high: 1084 hPa (Siberia, 1968)—extreme cold, calm conditions

Altitude Effects:

• Sea level: 101.3 kPa (14.7 PSI)
• Denver (1,600 m): 83 kPa (12 PSI)—17% lower pressure
• Mount Everest (8,849 m): 33 kPa (4.8 PSI)—1/3 sea-level pressure
• Airplane cabin (2,400 m equivalent): 75-80 kPa (11-12 PSI)
• Commercial jet cruise altitude (10,700 m): Outside pressure ~26 kPa (3.8 PSI)

Automotive and Transportation

Tire Pressure (kPa/PSI):

• Passenger car: 200-250 kPa (30-36 PSI)
• SUV/Truck: 240-280 kPa (35-40 PSI)
• Bicycle road tire: 550-850 kPa (80-120 PSI)
• Bicycle mountain tire: 170-310 kPa (25-45 PSI)
• Motorcycle: 200-290 kPa (29-42 PSI)
• Heavy truck: 550-830 kPa (80-120 PSI)
• Aircraft tire: 1,000-1,500 kPa (145-220 PSI)—extreme pressure for weight support

Engine Systems:

• Oil pressure (idle): 70-140 kPa (10-20 PSI)
• Oil pressure (highway): 280-410 kPa (40-60 PSI)
• Turbocharger boost: 50-150 kPa (7-22 PSI) above atmospheric = 150-250 kPa absolute
• Fuel rail pressure (gasoline direct injection): 5,000-20,000 kPa (725-2,900 PSI) = 5-20 MPa
• Common rail diesel: 160,000 kPa (23,200 PSI) = 160 MPa—ultra-high pressure

Materials Engineering (MPa/GPa)

Tensile Strength (maximum stress before failure):

• Aluminum 6061-T6: 310 MPa (45,000 PSI)
• Structural steel (mild): 400-550 MPa (58,000-80,000 PSI)
• High-strength steel: 760-1,500 MPa (110,000-220,000 PSI)
• Titanium alloy: 900-1,200 MPa (130,000-175,000 PSI)
• Carbon fiber composite: 600-1,000 MPa (87,000-145,000 PSI)
• Spider silk: ~1,000 MPa (145,000 PSI)—nature's strongest fiber
• Piano wire: 2,200 MPa (320,000 PSI)

Compressive Strength (resistance to crushing):

• Concrete (residential): 20-30 MPa (2,900-4,350 PSI)
• Concrete (high-strength): 50-100 MPa (7,250-14,500 PSI)
• Brick: 10-40 MPa (1,450-5,800 PSI)
• Granite: 100-250 MPa (14,500-36,250 PSI)
• Human bone (femur): 170 MPa (24,600 PSI)

Young's Modulus (elastic stiffness in GPa):

• Rubber: 0.01-0.1 GPa (very flexible)
• Nylon: 2-4 GPa
• Aluminum: 69 GPa
• Titanium: 116 GPa
• Steel: 200 GPa
• Silicon carbide: 450 GPa (extremely stiff ceramic)
• Diamond: 1,050 GPa (stiffest known material)

Hydraulic and Pneumatic Systems

Hydraulic Pressure:

• Hydraulic car jack: 10-20 MPa (1,450-2,900 PSI)
• Power steering: 7-14 MPa (1,000-2,000 PSI)
• Excavator hydraulics: 25-35 MPa (3,625-5,075 PSI)
• Industrial hydraulic press: 70-140 MPa (10,000-20,000 PSI)
• Waterjet cutter: 300-400 MPa (43,500-58,000 PSI)—cuts steel/stone

Pneumatic Systems:

• Air compressor (shop): 620-830 kPa (90-120 PSI)
• Pneumatic tools: 620 kPa (90 PSI) typical operating pressure
• HVAC ductwork: 0.1-2.5 kPa (0.4-10 inches water)—very low pressure
• Blast furnace: 300-400 kPa (43-58 PSI)
• Pipeline natural gas: 5,000-10,000 kPa (725-1,450 PSI) = 5-10 MPa

Vacuum Measurements (Below Atmospheric)

Vacuum Levels (absolute pressure):

• Rough vacuum: 100,000-10,000 Pa (100-10 kPa) = 0.99-0.1 atm
• Medium vacuum: 10,000-0.1 Pa (10 kPa to 0.1 Pa)
• High vacuum: 0.1-10⁻⁵ Pa
• Ultra-high vacuum (UHV): 10⁻⁵ to 10⁻⁹ Pa—semiconductor manufacturing
• Extreme high vacuum: <10⁻⁹ Pa—particle accelerators, space simulation
• Outer space (low Earth orbit): ~10⁻⁴ Pa
• Interstellar space: ~10⁻¹⁴ Pa

Vacuum Applications:

• Vacuum cleaner: ~80 kPa absolute (20 kPa below atmospheric)
• Vacuum packaging: 0.1-1 kPa—food preservation
• Freeze dryer: 10-100 Pa—pharmaceutical/food processing
• Electron microscope: 10⁻⁴ to 10⁻⁶ Pa—high vacuum for electron beam
• Mass spectrometer: 10⁻⁵ to 10⁻⁷ Pa

Sound Pressure and Acoustics

Sound Pressure Levels (Pa and dB SPL):

• Threshold of hearing: 0.00002 Pa = 20 μPa = 0 dB SPL
• Whisper: 0.0002 Pa = 200 μPa = 20 dB SPL
• Quiet library: 0.002 Pa = 2,000 μPa = 40 dB SPL
• Normal conversation: 0.02 Pa = 20,000 μPa = 60 dB SPL
• Busy traffic: 0.2 Pa = 200,000 μPa = 80 dB SPL
• Chainsaw: 2 Pa = 2,000,000 μPa = 100 dB SPL
• Rock concert: 20 Pa = 120 dB SPL
• Jet engine (30m away): 200 Pa = 140 dB SPL—threshold of pain
• Krakatoa eruption (160 km away): ~20,000 Pa = 180 dB SPL—eardrums rupture

Note: Sound pressure is measured in pascals, but decibels (dB SPL) use logarithmic scale: dB SPL = 20 log₁₀(P/P₀), where P₀ = 20 μPa.

Common Uses Across Industries

Scientific Research

• Standard unit: All pressure measurements in scientific papers reported in Pa/kPa/MPa
• Chemistry: Reaction pressures, gas laws (PV = nRT with P in pascals)
• Physics: Fluid dynamics, thermodynamics, material stress analysis
• Geology: Rock formation pressures, subsurface fluid pressures (MPa)

Meteorology and Climate Science

• Weather maps: Isobars labeled in hectopascals (hPa) or millibars (mbar)
• Barometric pressure: Reported in hPa worldwide (except US uses inHg)
• Climate modeling: Atmospheric pressure fields in kPa/hPa
• Aviation weather: Altimeter settings (US still uses inches Hg, elsewhere hPa)

Civil and Structural Engineering

• Concrete specifications: Compressive strength in MPa (20-100 MPa typical)
• Soil bearing capacity: kPa (50-300 kPa for different soil types)
• Wind load calculations: kPa (0.5-2 kPa for typical buildings)
• Snow load: kPa (0.5-5 kPa depending on snow depth/density)

Mechanical Engineering

• Stress analysis: Component stresses in MPa
• Pressure vessels: Design pressure in MPa, tested at 1.5× design pressure
• Piping systems: Operating pressure in kPa/MPa
• Bearing pressure: Contact stress in MPa (roller bearings 1,000-3,000 MPa)

Aerospace Engineering

• Cabin pressure: 75-80 kPa at cruise altitude (equivalent to 2,400 m elevation)
• Structural loads: Wing loading, fuselage stress in MPa
• Propulsion: Turbine blade stress, combustion chamber pressure (MPa)
• Altitude testing: Vacuum chambers simulating high-altitude pressure (kPa)

Medical and Biomedical

• Blood pressure: Still measured in mmHg (120/80 mmHg = 16/10.7 kPa) for historical reasons
• Respiratory pressure: Ventilators use kPa or cm H₂O
• Hyperbaric chambers: 200-300 kPa (2-3 atmospheres absolute)—wound healing, decompression
• Intraocular pressure: mmHg (glaucoma diagnosis)

HVAC and Building Systems

• Duct pressure: 100-2,500 Pa—fan static pressure
• Building pressurization: 2-25 Pa—positive pressure to prevent infiltration
• Filter pressure drop: 50-250 Pa—resistance across air filters
• Natural gas pressure (residential): 1.7-2.8 kPa (7-11 inches water)

Conversion Guide

Pascal to Other Units

Pascal to Kilopascal (kPa):

• Formula: kPa = Pa ÷ 1,000
• Example: 250,000 Pa = 250 kPa
• Use: Most practical engineering applications

Pascal to Megapascal (MPa):

• Formula: MPa = Pa ÷ 1,000,000
• Example: 50,000,000 Pa = 50 MPa
• Use: Material strength, high-pressure hydraulics

Pascal to Bar:

• Formula: bar = Pa ÷ 100,000
• Example: 500,000 Pa = 5 bar
• Use: European industrial, diving

Pascal to PSI:

• Formula: PSI = Pa × 0.000145038 (or Pa ÷ 6,894.76)
• Example: 200,000 Pa = 29.0 PSI
• Use: US/UK tire pressure, industrial

Pascal to Atmosphere (atm):

• Formula: atm = Pa ÷ 101,325
• Example: 202,650 Pa = 2.00 atm
• Use: Diving, gas storage

Pascal to mmHg (Torr):

• Formula: mmHg = Pa × 0.00750062 (or Pa ÷ 133.322)
• Example: 101,325 Pa = 760 mmHg
• Use: Blood pressure, vacuum systems

Pascal to Hectopascal (hPa):

• Formula: hPa = Pa ÷ 100
• Example: 101,325 Pa = 1,013.25 hPa
• Use: Meteorology (identical to millibar)

Quick Mental Math Approximations

Pa to kPa (exact):

• Move decimal point 3 places left
• 220,000 Pa = 220 kPa

kPa to PSI (~1/7 rule):

• Divide kPa by 7 for approximate PSI
• 210 kPa ÷ 7 ≈ 30 PSI (actual: 30.5 PSI)
• More precise: kPa × 0.145 = PSI

PSI to kPa (~7× rule):

• Multiply PSI by 7 for approximate kPa
• 30 PSI × 7 = 210 kPa (actual: 207 kPa)
• More precise: PSI × 6.895 = kPa

Bar to PSI (~14.5× rule):

• 1 bar ≈ 14.5 PSI
• 2 bar ≈ 29 PSI
• Exact: 1 bar = 14.50377 PSI

Atmospheric pressure equivalents (memorize):

• 1 atm = 101.325 kPa ≈ 101 kPa ≈ 100 kPa (rough)
• 1 atm = 14.7 PSI ≈ 15 PSI (rough)
• 1 atm = 1.01325 bar ≈ 1 bar (very close)

Conversion Table Reference

From	To PSI	To kPa	To bar	To atm	To mmHg
1 Pa	0.000145	0.001	0.00001	0.00000987	0.0075
1 kPa	0.145	1	0.01	0.00987	7.5
1 MPa	145.0	1,000	10	9.87	7,501
1 bar	14.50	100	1	0.987	750.1
1 PSI	1	6.895	0.069	0.068	51.71
1 atm	14.696	101.325	1.013	1	760.0
1 mmHg	0.0193	0.133	0.00133	0.00132	1

Common Conversion Mistakes

Mistake 1: Forgetting Metric Prefixes

Wrong: "Concrete strength is 30 Pa" (would crumble instantly) Right: "Concrete strength is 30 MPa" (30,000,000 Pa)

Why it matters: Three orders of magnitude error. Always include prefix (k, M, G) in engineering specs.

Mistake 2: Confusing Gauge vs Absolute Pressure

Wrong: "Tire pressure 220 kPa" interpreted as 220 kPa total Right: "Tire pressure 220 kPa gauge" = 220 + 101 = 321 kPa absolute

Why it matters:

• Gauge pressure: Pressure above atmospheric (PSI gauge = PSIG)
• Absolute pressure: Total pressure including atmospheric (PSI absolute = PSIA, kPa absolute)
• Tire gauges read gauge pressure; thermodynamic calculations need absolute pressure

Mistake 3: Using Wrong PSI Conversion Factor

Wrong: PSI × 7 = kPa (gives 7,000 Pa, not 6,895 Pa) Right: PSI × 6.895 = kPa (or PSI × 6,894.76 for precision)

Why it matters: 1.5% error accumulates in multi-step calculations. Use 6.895 for accuracy, not 7.

Mistake 4: Mixing kPa and hPa

Wrong: "Weather pressure is 1013 kPa" (would be 10× atmospheric pressure—impossible) Right: "Weather pressure is 1013 hPa" = 101.3 kPa

Why it matters:

• hPa (hectopascal) = 100 Pa = used in meteorology
• kPa (kilopascal) = 1,000 Pa = used in engineering
• 1 hPa = 0.1 kPa (factor of 10 difference)

Mistake 5: Ignoring Altitude Corrections

Wrong: Using 101.3 kPa for atmospheric pressure at Denver (1,600 m elevation) Right: Denver atmospheric pressure ≈ 83 kPa (about 17% lower than sea level)

Why it matters: HVAC, engine performance, boiling point calculations all affected by altitude. Pressure drops ~1 kPa per 80 m elevation gain near sea level.

Mistake 6: Confusing Stress and Pressure Units

Wrong: Reporting material stress in PSI when spec requires MPa Right: Converting properly: 50,000 PSI = 345 MPa

Why it matters: International standards (ISO, ASTM) increasingly require MPa. Must convert legacy PSI data correctly for compliance.