Convert psi, bar, kPa, atmospheres, Torr, mercury units, and other pressure measures. The conversion changes the unit while preserving the pressure reference used by your original measurement.
How to use this calculator
Enter the measurement and select both units. A tire gauge reading in psi can be expressed in bar using the same gauge reference. When comparing two specifications, check whether each one is gauge, absolute, or differential pressure before comparing their numbers.
Gauge pressure and absolute pressure
Gauge pressure is measured relative to a reference such as ambient atmospheric pressure. Absolute pressure is measured relative to vacuum. Changing psi to kPa does not change one reference into the other. To find absolute pressure from gauge pressure, add the actual reference pressure in matching units.
One standard atmosphere is defined as 101,325 Pa; actual local atmospheric pressure varies. A Torr is one 760th of a standard atmosphere. The conventional mercury options use fixed conversion factors. Conventional mmHg and Torr are very close, but they are not exactly the same definition.
Examples
A pressure specification
2.4 bar ≈ 34.80905706 psi. If the input was gauge pressure, the result is also gauge pressure.
A weather reading
1,013.25 hPa = 101.325 kPa = 1 atm. Millibars and hectopascals have the same numeric value.
Formula
target pressure = source pressure × source factor / target factor
1 bar = 100,000 Pa = 100 kPa
1 standard atmosphere = 101,325 Pa
absolute pressure = gauge pressure + reference pressure
Precision and interpretation
Negative inputs can describe a gauge pressure or pressure difference, but not a physical negative absolute pressure. This unit converter does not infer the reference. Mercury-column temperatures and material conventions matter in precision work; use the explicitly labeled conventional factors only when appropriate.
Definitions and further reading
Unit and quantity reference provides the underlying definitions. The examples above are worked calculations for this tool.