Pressure Converter

How it works

Every pressure unit is defined as some number of pascals (newtons per square metre). The calculator multiplies your value by the size of the unit it is in to get pascals, then divides by the size of the unit you want.

The standard atmosphere is exactly 101,325 Pa and the bar exactly 100,000 Pa. A pound per square inch is the pound-force (0.45359237 kg × 9.80665 m/s² = 4.4482216152605 N) over a square inch (0.00064516 m²), which is 6,894.757 Pa. The Torr is defined as 1/760 of an atmosphere; the millimetre and inch of mercury use the conventional density of mercury at 0 °C, so 760 Torr is 759.9999 mmHg, a difference of one part in seven million.

The conversion factor is what one unit of the 'from' unit is worth in the 'to' unit, so you can apply it to other readings by hand. The table lists the same pressure in every unit the converter knows.

Formula

pascals   = value × (size of the from unit in Pa)
converted = pascals ÷ (size of the to unit in Pa)
factor    = size of from unit ÷ size of to unit

1 atm = 101,325      1 bar = 100,000      1 psi = 4.4482216152605 / 0.00064516
1 Torr = 101,325/760 1 mmHg = 133.322387415  1 inHg = 3,386.389
1 inH₂O = 249.0889   1 kgf/cm² = 98,066.5

Example

1 atm, the default, is 101,325 Pa, which is 101,325 ÷ 6,894.757 = 14.695949 psi. The factor from atm to psi is 14.6959487755.

The table shows the same atmosphere as 101.325 kPa, 1.01325 bar, 760 Torr, 29.921252 inHg and 1.033227 kgf/cm². A tyre at 32 psi is 32 × 6.894757 = 220.632233 kPa, or 2.206322 bar.

Assumptions and limitations

• All values are converted as absolute multiples of the pascal. Gauge and absolute pressure are not distinguished: a gauge reading converts to the same gauge reading in the other unit, and a negative (vacuum gauge) value is converted as entered.
• psi uses the exact pound-force (standard gravity 9.80665 m/s²) and the exact inch, giving 6,894.757293 Pa.
• mmHg and inHg are the conventional values at 0 °C (133.322387415 Pa and 3,386.389 Pa); the inch of water is the conventional value 249.0889 Pa (water at 1,000 kg/m³ under standard gravity). Values at other temperatures differ by a few parts in a thousand.
• Torr is exactly 1/760 atm. It differs from the conventional mmHg by about one part in seven million.
• Results are shown to six decimal places; very small values may display as 0 even though the conversion is computed in full precision.

Frequently asked questions