Pressure Converter
Convert between pascals, bars, psi, atmospheres and millimetres of mercury for weather, tyres and engineering.
Written by Rahman · Last reviewed
Quick answer
Pressure conversion runs through the pascal, one newton per square metre. One bar is exactly 100,000 pascals, one standard atmosphere is 101,325 pascals, and one psi is 6,894.76 pascals. Tyre pressures quoted in bar and psi differ by a factor of about 14.5.
| Pascal (Pa) | 1 |
| Kilopascal (kPa) | 0.001 |
| Megapascal (MPa) | 0.000001 |
| Hectopascal (hPa) | 0.01 |
| Bar (bar) | 0.00001 |
| Millibar (mbar) | 0.01 |
| Pound per square inch (psi) | 0.0001450377377 |
| Atmosphere (atm) | 0.000009869232667 |
| Torr (Torr) | 0.007500616827 |
| Millimetre of mercury (mmHg) | 0.007500615758 |
| Inch of mercury (inHg) | 0.0002952998016 |
About the Pressure Converter
Pressure is force applied over an area. This converter handles pascals, kilopascals and bars alongside pounds per square inch (psi), atmospheres and millimetres of mercury.
It is used in weather forecasting, tyre inflation, diving, plumbing and engineering, where pressure is reported in many different units around the world.
Gauge pressure and absolute pressure differ by an atmosphere
Nearly every pressure reading in everyday use is a gauge reading: measured relative to the surrounding air rather than to a vacuum. A tyre gauge showing zero on a flat tyre does not mean there is no pressure inside; it means the pressure inside matches the pressure outside.
Absolute pressure adds the atmosphere back. One standard atmosphere is 101,325 Pa, or about 14.696 psi, so a tyre inflated to 32 psi gauge is at roughly 46.7 psi absolute. The units are marked psig and psia where the distinction matters, and mixing them introduces a full atmosphere of error.
- Tyre pressures, blood pressure and most industrial gauges are gauge readings. Weather and vacuum measurements are absolute.
- This converter handles the units themselves; whether a figure is gauge or absolute is a property of how it was measured, not of the unit it is written in.
- The error is constant rather than proportional, so it matters most at low pressures: at 5 psi gauge, confusing the two is a threefold mistake.
Bar, atmosphere and psi are close but not equal
Bar was defined as a round metric quantity (exactly 100,000 Pa), while the standard atmosphere is 101,325 Pa, the historical average sea-level pressure. They sit 1.32% apart, close enough to be used interchangeably in casual conversation and far enough apart to matter in calibration.
In psi terms, one bar is about 14.504 psi and one atmosphere about 14.696 psi. Weather reporting adds a further wrinkle: hectopascals and millibars are numerically identical, which is why forecasts switched between them without any of the numbers changing.
- Torr and millimetres of mercury are also near-identical but not defined the same way, differing far below any practical measurement.
- Inches of mercury appear in US aviation and weather reporting, and in vacuum work.
- Where precision matters, convert through pascals rather than chaining approximate conversions.
Frequently Asked Questions
How many psi are in a bar?
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One bar equals about 14.5038 psi, and one psi equals roughly 0.0689 bar.
What is standard atmospheric pressure?
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Standard atmospheric pressure at sea level is 101,325 pascals, equal to 1 atmosphere or about 14.7 psi.
What units are used for tyre pressure?
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Tyre pressure is usually given in psi, bar or kilopascals depending on the country and vehicle.