Pressure Converters

30 converters, all running in your browser.

The pascal is the SI unit of pressure — one newton per square metre — and it is inconveniently small for most practical use, which is why almost every field uses something else.

Weather is reported in hectopascals or millibars, which are the same size: standard atmospheric pressure is 1013.25 hPa. Tyres are inflated in psi or bar, where 1 bar is almost exactly one atmosphere and psi is about 14.5 per bar. Diving works in atmospheres or bar because the numbers map neatly onto depth: seawater adds roughly one atmosphere every 10 metres. Medicine uses millimetres of mercury for blood pressure, a unit that literally describes the height of a mercury column and survives long after the mercury sphygmomanometer stopped being used.

One distinction worth holding: gauge pressure measures above atmospheric, absolute pressure measures from vacuum. A tyre reading 32 psi is 32 psi *gauge* — about 46.7 psi absolute. These converters work in the units as quoted, so compare like with like.

Conversion factors

From	To	Multiply by
Pascals	Kilopascals	0.001
Pascals	Bar	1.0000e-5
Pascals	Atmospheres	9.8692e-6
Pascals	PSI	1.4504e-4
Pascals	mmHg	0.0075006158
Kilopascals	Pascals	1000
Kilopascals	Bar	0.01
Kilopascals	Atmospheres	0.0098692327
Kilopascals	PSI	0.14503774
Kilopascals	mmHg	7.5006158
Bar	Pascals	100000
Bar	Kilopascals	100
Bar	Atmospheres	0.98692327
Bar	PSI	14.503774
Bar	mmHg	750.06158
Atmospheres	Pascals	101325
Atmospheres	Kilopascals	101.325
Atmospheres	Bar	1.01325
Atmospheres	PSI	14.695949
Atmospheres	mmHg	759.99989

Tyre Pressure, and Why the Numbers Differ

The pressure on the tyre sidewall is a maximum, not a recommendation. The figure to use is on the driver's door pillar or in the handbook, and it is usually lower — often 32–36 psi against a sidewall maximum of 44 or more.

Pressure also rises with temperature, roughly 1 psi per 10 °F. A tyre checked cold at 32 psi reads 35 or more after a motorway run, which is why the instruction is always to check cold.

Unit	Typical car tyre
psi	32–36
bar	2.2–2.5
kPa	220–250

Weather Pressure

A barometer reading below 1000 hPa suggests unsettled weather and above 1020 hPa settled; the rate of change matters more than the value. A fall of 3 hPa in three hours is a meaningful signal of an approaching front.

Aviation uses inches of mercury in the US and hectopascals almost everywhere else, and the altimeter setting has to be converted between them on any transatlantic flight.

← All unit converter categories

All 30 converters

Conversion factors

Tyre Pressure, and Why the Numbers Differ

Weather Pressure