Pressure is quoted in wildly different units depending on the field — pascals in physics, psi in plumbing and tyres, atmospheres in chemistry, and mmHg or inHg in weather and medicine. This reference converts any pressure into every supported unit at once, using exact factors.
Where each unit comes from
Every field that measures pressure developed units scaled to what is practical for its context:
| Unit | Field | Typical range |
|---|---|---|
| Pascal (Pa) / kPa | Physics, engineering, SI standard | Atmospheric ~101,325 Pa |
| Bar / millibar (hPa) | Meteorology, fluid mechanics | Atmospheric ~1,013 mbar |
| psi | Plumbing, tyres, US engineering | Tyre pressure ~30–35 psi |
| atm | Chemistry, gas laws | Standard atmosphere = 1 atm |
| mmHg | Clinical medicine (blood pressure) | Normal BP ~120/80 mmHg |
| torr | Vacuum science, chemistry | Vacuum < 1 torr |
| inHg | US aviation and weather | Sea-level pressure ~29.92 inHg |
The millibar and the hectopascal (hPa) are numerically identical — 1 mbar = 1 hPa = 100 Pa — used interchangeably in meteorology.
How it works
Each unit stores an exact number of pascals per unit, with the pascal (one newton per square metre) as the SI base. Conversion is two steps:
pascals = value × pascalsPerUnit[from]
result = pascals ÷ pascalsPerUnit[to]The anchor points are the standard atmosphere 1 atm = 101325 Pa, the 1 bar = 100000 Pa (exact), and 1 psi = 6894.757293 Pa. The torr is defined as exactly 1/760 atm, and the conventional millimetre of mercury (133.322387415 Pa) is almost — but not exactly — equal to it.
Worked examples
Tyre pressure: A car tyre inflated to 32 psi converts to 32 × 6894.757 ÷ 100,000 ≈ 2.21 bar. Most European tyre gauges read in bar, so 2.2 bar is the equivalent to set.
Blood pressure: A reading of 120 mmHg systolic converts to 120 × 133.322 ≈ 15,999 Pa ≈ 16.0 kPa. Some European clinical settings report blood pressure in kPa.
Weather forecast: A barometer reading of 1,013 hPa is standard sea-level atmospheric pressure, equivalent to 29.92 inHg — the values you see in US aviation weather reports (METAR/TAF).
Vacuum systems: A rough vacuum at 1 torr is approximately 133 Pa or about 0.00132 atm. High vacuum in the range of millitorr is common in electron microscopes and sputter-coating equipment.
Ties between systems
One atmosphere ties the systems together: 1 atm = 101,325 Pa = 1.01325 bar = 14.696 psi = 760 torr = 29.921 inHg. This anchor makes cross-system sanity checks easy — if your converted value differs from the atmospheric equivalents by the expected ratio, the conversion is correct.
All results in scientific notation when very large or very small. Everything runs locally in your browser.