Convert pressure (bar, psi, pascal, atm)

The value is multiplied by its factor to the pascal, then divided by the target unit's factor. The psi (pound-force per square inch) comes from the imperial system; the conventional millimetre of mercury is 133.322387415 Pa. A tyre pressure shown in bar therefore reads in psi without going through an approximate table.

p(Pa) = x × kfrom ; y = p(Pa) / kto

1 bar = 100,000 Pa

1 atm = 101,325 Pa

The pascal is the SI unit of pressure. The bar is not an SI unit but remains accepted, notably in meteorology as the hectopascal. The psi dominates in the English-speaking world, including for tyres. Whether the figures are gauge or absolute depends on your source: this tool does not distinguish between them.

Value

The pressure alone, without the unit.

From

Unit of the pressure you entered. The default is bar.

To

Unit of the result. The default is psi, common for tyres.

Assumptions

• 1 bar = 100,000 Pa exactly.
• 1 atm = 101,325 Pa, the standard atmosphere.
• mmHg is the conventional millimetre of mercury.

Limits

• No distinction between absolute, gauge and differential pressure.
• No altitude or temperature correction.
• Tyre pressure is specified cold: the conversion does not correct for heating.

2.4 bar and 34.8 psi describe the same pressure. Watch what kind of measurement it is: a tyre gauge reads gauge pressure, above the surrounding atmosphere, while an absolute pressure includes that atmosphere. A gap of about 1 bar between two sources usually comes from that, not from a conversion error.

• Taking 1 bar as 1 atmosphere.

  1 bar = 100,000 Pa, 1 atm = 101,325 Pa, a 1.3% difference.

• Confusing psi with psig.

  psig is explicitly gauge pressure; plain psi may mean absolute depending on context.

• Inflating a tyre to the value read when hot.

  The recommended pressure is checked cold; warm air raises the reading.

• Energy converterEvery energy routes through the joule. A kilowatt-hour is exactly 3.6 million joules, and a food kilocalorie 4,184 joules.
• Power converterEvery power routes through the watt. Metric horsepower is 735.49875 W and mechanical horsepower 745.7 W: two different units sharing one everyday name.
• Weight (mass) converterEveryday speech says “weight”; SI speaks of mass. Conversion goes through the kilogram. The pound (lb) is 0.45359237 kg exactly, a NIST factor, not a weighing on Earth.
• Area converterFactors are SI areas and the international acre. A hectare is 10,000 m² exactly. The acre used here is not the arpent, nor a local survey acre.
• Angle converterEvery angle routes through the radian, the SI unit. A half turn is π radians, 180 degrees or 200 gradians: three ways of describing the same opening.
• Data storage converterThe maths routes through the bit. Decimal prefixes (1 kB = 1,000 bytes) and binary ones (1 KiB = 1,024 bytes) are handled separately, as IEC 80000-13 specifies.

Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

• NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
• The International System of Units (SI) — Bureau international des poids et mesures (BIPM)