Pressure Converter
Convert pascal, bar, PSI and atmospheres.
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The Pressure Converter moves a reading between pascal, kilopascal, bar, PSI and standard atmosphere. Typical jobs are turning a car's recommended tyre pressure from psi into bar, checking a compressor or pump rating, and converting textbook values between kPa and atmospheres.
How to use it
Put the reading in Value, choose its unit under From, choose the target under To and click Convert. The tool expresses your value in pascals, then divides by the target unit's size. You get the headline answer plus the same pressure in the other four units, each rounded to six decimals.
Units and their sizes in pascals
| Unit | Pascals |
|---|---|
| 1 kilopascal (kPa) | 1,000 |
| 1 bar | 100,000 |
| 1 PSI | 6,894.757 |
| 1 atmosphere (atm) | 101,325 |
A pascal is one newton per square metre, a very small pressure, which is why kPa and bar are more common in practice. The bar and the standard atmosphere are both fixed by definition, and PSI means pound-force per square inch. From these: 1 atm = 1.01325 bar = 14.695949 PSI, and 1 bar = 14.503774 PSI.
Worked example: a 32 psi tyre in bar
Many car door placards give tyre pressure in psi, while some inflators and European manuals use bar or kPa. Enter 32, From PSI, To bar:
32 × 6,894.757 = 220,632.224 Pa; 220,632.224 ÷ 100,000 = 2.206322 bar
The other rows read 220.632224 kPa and 2.177471 atm. In practice you would set the inflator to 2.2 bar or 221 kPa. Going the other way, a manual that specifies 2.5 bar is asking for 36.26 psi (250,000 ÷ 6,894.757).
Gauge pressure versus absolute pressure
A tyre gauge shows how far the pressure inside is above the air around it. That is gauge pressure, sometimes written psig. Absolute pressure adds the atmosphere back on, about 14.7 psi at sea level, so a tyre at 32 psi gauge is roughly 46.7 psi absolute. This converter only changes units; it never adds or removes atmospheric pressure, so convert gauge readings to gauge readings and absolute to absolute.
Absolute pressure is also what the gas laws use. In a tyre, whose volume barely changes, absolute pressure rises in proportion to absolute temperature in kelvin. Warming from 25 °C (298.15 K) to 45 °C (318.15 K) multiplies 46.7 psi absolute by about 1.067, giving roughly 49.8 psi absolute, or 35.1 psi on the gauge. That is why placard pressures are meant to be checked with cold tyres. The temperature converter gives the kelvin figures.
Units not in the list and how to reach them
- kgf/cm²: still printed on many compressor and pump gauges in India. One kgf/cm² is exactly 98.0665 kPa, so multiply by 98.0665 and enter the result as kilopascals. That makes 1 kgf/cm² about 14.22 PSI or 0.98 bar.
- hPa and millibar: weather reports use these. One hectopascal equals one millibar equals 100 Pa, so divide by 10 to get kPa; standard sea-level pressure is 1,013.25 hPa.
- mmHg: used for blood pressure and older barometers. One mmHg is about 133.322 Pa.
- Metres of water head: pump specifications often quote head. Ten metres of water is roughly 98 kPa, just under 1 bar.