Article — kPa to PSI Conversion Calculator
kPa to psi Conversion: From SI Pressure to the Imperial Pound
One kilopascal equals 0.145038 pounds per square inch. The reverse is 1 psi equals 6.89476 kPa. Both factors derive from the NIST definition of one pound-force per square inch as exactly 6,894.757 Pa, which in turn rests on the international pound (0.45359237 kg) and inch (0.0254 m) treaty values.
The conversion is the most-searched pressure conversion on the web because of the split between metric and imperial standards. American tire gauges, scuba shops, and machine-shop manuals stay with psi; the rest of the world prints kPa or bar. Translating takes one multiplication; getting the factor wrong by seven causes blown gaskets and under-inflated tires.
The kPa to psi conversion factor
The exact factor is 1 kPa = 0.14503773773 psi. NIST publishes this value to ten significant figures in Special Publication 811, the Guide for the Use of SI Units. The reciprocal is 1 psi = 6.89475729317 kPa. Both are exact under the SI definitions, not measurements, because the underlying pound and inch are fixed by international treaty.
The pascal is the SI unit of pressure: one newton per square metre. The kilopascal is a thousand pascals, the practical scale for everyday pressures. Atmospheric pressure runs around 100 kPa; tire pressure around 200 kPa; industrial hydraulics around 20,000 kPa.
The pascal was added to SI in 1971, named for the seventeenth-century French mathematician Blaise Pascal whose Treatise on the Equilibrium of Liquids (1654) laid out the principle that pressure applied to a confined fluid transmits equally in all directions. Every hydraulic system in modern engineering is a working demonstration of Pascal's principle.
Tire pressure in kPa and psi
Passenger car tires take 200 to 250 kPa (29 to 36 psi) when cold. Most US sedans specify 220 kPa (32 psi) for the front and rear; SUVs and light trucks run 240 to 260 kPa (35 to 38 psi). The door-jamb placard inside the driver's door prints both units, with kPa as the legally required metric value and psi as the consumer-facing display.
Tire pressure rises about 7 kPa (1 psi) per 10°C of temperature increase. A tire inflated to 220 kPa on a 5°C morning reads 240 kPa after highway driving. Recommended pressures are always cold pressures.
Some dual-scale gauges put kPa on the outer ring and psi on the inner ring, others reverse them. A misreading by a factor of seven (assuming kPa is psi) puts a passenger car tire at 30 kPa (4 psi) — flat enough to delaminate the sidewall on the first highway exit. Always verify which scale you are reading before inflating.
Weather, altitude, and atmospheric pressure
Standard sea-level atmospheric pressure is 101.325 kPa, equal to 14.696 psi or 1.013 bar. The BIPM lists this as the reference atmosphere for SI work. Weather services report sea-level pressure in hectopascals (hPa), where 1013.25 hPa equals the standard atmosphere. A high-pressure system might read 1025 hPa (102.5 kPa, 14.87 psi); a low-pressure storm system 980 hPa (98.0 kPa, 14.21 psi).
Pressure drops about 12 kPa per kilometer near sea level. Denver (1,600 m) sits at 84 kPa (12.2 psi). Mt Everest summit is 31 kPa (4.5 psi), low enough to require supplemental oxygen. Airliners pressurize cabins to 75 kPa (10.9 psi), equivalent to about 2,400 m.
- Sea level 101.325 kPa (14.696 psi, 1 atm)
- Denver (1,600 m) 84 kPa (12.2 psi)
- Mexico City (2,240 m) 78 kPa (11.3 psi)
- Cabin altitude (2,400 m) 75 kPa (10.9 psi)
- Mt Everest summit 31 kPa (4.5 psi)
- Cruising altitude (10,000 m) 26 kPa (3.8 psi)
- Mars surface (mean) 0.6 kPa (0.087 psi)
- Interplanetary vacuum ~0 kPa
Scuba and dive pressure in kPa
A standard aluminum 80 scuba tank holds 3,000 psi, equal to 207 bar or 20,700 kPa. European dive shops display bar; US shops still use psi. The discrepancy is one reason dive computers let the diver pick the unit in the settings menu. Water pressure adds 100 kPa (about 14.5 psi, or 1 bar) for every ten metres of depth, on top of the surface atmospheric pressure.
At 30 m depth, total absolute pressure on the diver is 400 kPa (58 psi, 4 bar). That fourfold compression limits no-decompression dive times and forces gas mixtures other than air for deeper work.
HVAC and refrigerant pressure
HVAC technicians work in both kPa and psi depending on the equipment vintage and the country. R-410A air conditioning systems run a low-side suction pressure of around 800 kPa (116 psi) and a high-side discharge pressure of around 2,800 kPa (406 psi) on a hot day. R-134A automotive systems run lower, with suction around 200 kPa (29 psi) and discharge around 1,400 kPa (203 psi).
European compressor manuals list ranges in kPa or bar; US units use psi. A reading of 250 psi on a US gauge translates to 1,724 kPa on a European data sheet, well within the normal high-side range.
When working with mixed-unit equipment, label the gauge with the operating range in both units. A piece of masking tape with "Low side: 700–900 kPa / 102–131 psi" stuck on the manifold removes the conversion from the troubleshooting loop and prevents mental-math errors at three in the morning on a service call.
Mental math for kPa to psi
The fast mental rule is to divide kPa by seven to estimate psi. The exact factor is 6.89476, so dividing by seven introduces a 1.5% error in the conservative direction (underestimating psi). For tire pressure work that is well inside the accuracy of the gauge itself. 210 kPa ÷ 7 = 30 psi (true: 30.5 psi). 280 kPa ÷ 7 = 40 psi (true: 40.6 psi).
Going the other way, multiply psi by seven to estimate kPa: 32 × 7 = 224 (true 220.6). For more accuracy, use 6.9: 32 × 6.9 = 220.8 kPa, within 0.1 of exact.
kPa ÷ 7 ≈ psi (error 1.5%)kPa × 0.145 = psi (error 0.04%)psi × 7 ≈ kPa (error 1.5%)psi × 6.9 ≈ kPa (error 0.07%)1 bar = 100 kPa = 14.5 psiCommon kPa to psi mistakes
The most common error is confusing absolute and gauge pressure. A tire gauge reads gauge pressure: zero on the gauge equals atmospheric pressure (about 101 kPa absolute). Engineering calculations and weather reports usually quote absolute pressure. A tire at 220 kPa gauge is at 321 kPa absolute, a 50% difference. Most kPa-to-psi conversions treat both sides the same way, so the conversion is unaffected, but the underlying meaning of the number depends on the reference.
The second mistake is unit-prefix confusion. kPa and MPa differ by 1,000. A hydraulic spec calling for 20 MPa (2,901 psi) is not the same as 20 kPa (2.9 psi); reading one as the other puts a hydraulic press a thousand times under-pressure.
Related pressure conversions
kPa connects to other pressure units through fixed factors: 1 kPa = 0.01 bar, 0.00987 atm, 7.50 mmHg, and 0.295 inches of mercury. Each shows up in a specific field — mmHg in medicine, inches of mercury in US weather, atm in chemistry. The kPa-to-psi conversion is one bridge in a network that traces back to the SI pascal.