Pressure converter
Convert between pascals, bar, psi, atmospheres and millimeters of mercury, then watch a gauge needle place your pressure against a car tyre, an espresso machine and the deep ocean.
That's about the same as a car tyre. Spread over a fingertip, that is like resting 2.345 kg on it.
What it means
How much pressure is that?
Tyre and tank figures are gauge pressure, measured above the surrounding air. Weather and altitude figures are absolute.
Every unit
Your pressure in every unit
Learn
Three things worth knowing
-
Bar to psi: add half again, twice
1 bar is 14.5 psi. For tyres, multiply by 15 and take off a little: 2 bar is 29 psi, 2.5 bar about 36 psi.
-
Torricelli and the mercury column
In 1643 Torricelli filled a tube with mercury, upturned it in a dish, and the column stopped falling at 760 mm. The air was holding it up, which is why one atmosphere is 760 mmHg.
-
Gauge pressure or absolute?
A tyre gauge reads zero in open air, because it measures above atmospheric pressure. A "2.3 bar" tyre is really at 3.3 bar absolute. Mixing the two ruins a calculation.
Shortcuts
Popular pressure conversions
Background
About pressure units
Pressure is force spread over an area. The SI unit is the pascal, one newton per square meter, which is tiny: everyday pressures run to hundreds of thousands of them. So weather uses hectopascals, engineers use bar, and the US uses psi.
Medicine still measures blood pressure in millimeters of mercury, the height of a mercury column the pressure can hold up.