Room for ChanceWhat it measures and where it is used
Pressure is force divided by area. It appears in tyres, weather and fluid systems. The pascal is one newton per square metre and honours Blaise Pascal. Bar, atmosphere and psi are different conventions. Torr is defined here as 1/760 of a standard atmosphere.
- Classification
- SI derived quantity
- SI unit
- Pa = kg·m⁻¹·s⁻²
- Dimension
- M L⁻¹ T⁻²
L: length; M: mass; T: time; Θ: temperature; N: amount of substance. The dimension symbol N is not the unit symbol for newton.
How it works
The calculation first converts to a common reference unit, then to the destination unit. Factors in the table show the reference value for one unit.
Example
1 bar ≈ 100,000 Pa
Available units
Reference unit: Pa
| Available units | Reference factor |
|---|---|
| Pa | 1 × x |
| kPa | 1,000 × x |
| MPa | 1,000,000 × x |
| hPa | 100 × x |
| bar | 100,000 × x |
| mbar | 100 × x |
| atm | 101,325 × x |
| Torr | 133.322368421 × x |
| psi | 6,894.75729317 × x |
Units, history and conventions
The International System of Units (SI) received its name in 1960. Since the 2019 revision, its definitions use fixed values of seven defining constants. SI base and derived quantities should not be confused with the different units used to express them.
IUPAC does not replace the SI: its Green Book standardises quantities, symbols and terminology in physical chemistry. Its predecessor was published in 1969. The mole is particularly important when counting specified chemical entities.