What the pressure converter does
Pressure is force spread over an area, and this converter switches a pressure value between six units: pascals, kilopascals, bar, pounds per square inch (psi), standard atmospheres and torr. Enter a number, pick the units, and press Convert. The value is converted through the pascal, the SI unit, and shown to up to 8 decimal places.
Conversion factors
| Unit | Symbol | In pascals | Status |
|---|---|---|---|
| Pascal | Pa | 1 | SI unit, 1 N/m² |
| Kilopascal | kPa | 1,000 | exact |
| Bar | bar | 100,000 | exact |
| Standard atmosphere | atm | 101,325 | exact by definition |
| Pound per square inch | psi | 6,894.757293168 | derived from lbf and inch |
| Torr | Torr | 133.322368421053 | 101,325 ÷ 760 |
The pascal is one newton per square meter, as set out in the BIPM SI Brochure. It's a tiny pressure, which is why weather reports use hectopascals and engineers use kilopascals or megapascals.
The standard atmosphere was fixed at exactly 101,325 Pa in 1954, close to average sea-level air pressure. The bar, exactly 100,000 Pa, is a round-number cousin that's common in Europe for tyres, scuba cylinders and weather (the millibar is a hectopascal). The torr is defined as 1/760 of an atmosphere, after the 760 mm column of mercury in Torricelli's barometer.
psi comes from the pound-force (4.4482216152605 N) over one square inch (0.0254² m²), giving 6,894.757293168… Pa. NIST Special Publication 811 lists all of these.
The torr factor is stored to 12 decimal places (133.322368421053), and every result is rounded to 12 significant figures before it's shown, so a round trip comes back clean: 760 Torr converts to exactly 101,325 Pa.
Quick reference
| From | To | Multiply by |
|---|---|---|
| psi | kPa | 6.894757 |
| kPa | psi | 0.145038 |
| bar | psi | 14.5038 |
| psi | bar | 0.0689476 |
| atm | kPa | 101.325 |
| atm | psi | 14.6959 |
| bar | atm | 0.986923 |
| torr | kPa | 0.133322 |
Worked examples
- Car tyre at 32 psi: 32 × 6.894757 = 220.63 kPa, which is about 2.2 bar. European door placards often give 2.2 bar, or 220 kPa.
- A full scuba cylinder at 200 bar: 200 × 14.5038 = 2,900.75 psi.
- A bicycle tyre at 35 psi in bar: 2.413 bar.
- Blood pressure of 120 mmHg in kPa: using torr as a stand-in for mmHg, 120 × 0.133322 = 16.00 kPa.
Gauge vs absolute pressure
Most everyday gauges, including tyre gauges and pressure cookers, read gauge pressure: how far above the surrounding air pressure you are. A flat tyre reads 0 psi even though the air inside is at about 14.7 psi absolute. Engineering datasheets sometimes mark the difference with psig and psia, or "bar(g)" and "bar(a)".
This converter doesn't know which one you have. It converts 32 psi gauge to 220.63 kPa gauge. If you need absolute pressure, add atmospheric pressure (101.325 kPa, 1.01325 bar or 14.696 psi at sea level) after converting, and use the same reference on both sides of any comparison.
Related converters
- Force converter: newtons, pound-force and kilogram-force, the top half of every pressure unit.
- Area converter: the bottom half, from square inches to square meters.
- Temperature converter: gas pressure and temperature usually travel together.
- Energy converter: joules, kWh, calories and BTU.
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