🎈 Pressure

Bar to MPa

Convert bar to megapascals, psi, kPa, atmospheres, torr and kilograms per square centimetre. Enter a value, choose the units, then press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed 28 October 2026 · Editorial standards · Report an error

About the Bar to MPa

One bar is exactly 100,000 pascals, and one megapascal is one million pascals, so 1 bar is 0.1 MPa. The bar is convenient because it is almost exactly one atmosphere — 1 atm is 1.01325 bar — which is why weather reports and scuba tanks use it alongside the older atmosphere.

MPa is the preferred unit in engineering because it keeps numbers manageable for high pressures: a hydraulic system at 25 MPa is 250 bar. PSI remains common in the US and in tyre and plumbing specifications; 1 psi is 0.0689476 bar.

How the calculation works

1 bar = 0.1 MPa = 100 kPa = 100,000 Pa.
1 psi = 0.0689476 bar = 0.00689476 MPa.
1 atm = 1.01325 bar = 0.101325 MPa.
1 torr = 1 mmHg = 0.00133322 bar.
1 kg/cm² = 0.980665 bar.

Reference values

Common pressure values
Pressure	Bar	MPa	PSI
Atmospheric	1.013	0.1013	14.70
Car tyre	2.2	0.22	31.9
Scuba tank	200	20	2,901
Hydraulic system	250	25	3,626
Vacuum (rough)	0.001	0.0001	0.0145

Worked example: three everyday pressures

A scuba cylinder filled to 200 bar is 20 MPa, or 2,901 psi. A car tyre at 2.2 bar is 0.22 MPa and 31.9 psi. A hydraulic system at 25 MPa is 250 bar and 3,626 psi. To reverse the direction, divide psi by 14.5038 to get bar, then divide by 10 to get MPa.

The bar is not an SI unit, but it is accepted for use with SI because it is a convenient multiple close to atmospheric pressure. That is why weather maps, diving tables and older pressure gauges still use it, while engineering drawings increasingly specify MPa to stay coherent with the pascal.

Gauge, absolute and differential pressure

A tyre gauge reading 2.2 bar is a gauge pressure: it measures the difference between the tyre and the surrounding air. Absolute pressure adds atmospheric pressure, so the same tyre holds about 3.2 bar absolute at sea level. Scuba and diving tables often quote gauge pressure, while vacuum systems, chemistry and meteorology usually use absolute, because a negative gauge reading would otherwise make no sense.

Most instruments state which convention they use, but the label is easy to miss. A gauge marked “bar” with no suffix is normally gauge, and one marked “bara” or “bar abs” is absolute. In a vacuum, the two differ by a full atmosphere, which is the entire scale, so mixing them up produces a result that is wrong by 100%.

Frequently asked questions

Is bar the same as atmospheres?

Almost. 1 atm = 1.01325 bar, a difference of about 1.3%. For tyre pressure that is negligible; for calibration it is not.

Why use MPa instead of bar?

MPa is the SI-consistent multiple of the pascal and is standard in engineering drawings. It also keeps high-pressure numbers short: 25 MPa rather than 250 bar.

Is kg/cm² the same as bar?

No. 1 kg/cm² = 0.980665 bar, about 2% lower. The unit is often written kgf/cm² to make the distinction clear.

Why is bar still used when pascal is the SI unit?

The bar is a convenient multiple close to atmospheric pressure and is accepted for use with SI. MPa is preferred in engineering because it is a coherent decimal multiple of the pascal.

What is the difference between gauge and absolute pressure?

Gauge pressure is measured relative to the surrounding atmosphere; absolute pressure is measured relative to a perfect vacuum. Absolute pressure equals gauge pressure plus atmospheric pressure.

Sources and standards

The bar is exactly 100,000 Pa and the megapascal exactly 1,000,000 Pa, so the conversion is a factor of ten with no rounding involved. NIST SP 811 documents the pascal and its multiples, and the page also gives the psi equivalent for context.