Pascal
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The pascal (symbol Pa) is the SI unit of pressure. It is equivalent to one newton per square metre. The unit is named after Blaise Pascal, the eminent French mathematician, physicist and philosopher.
The same unit is also used for stress, Young's modulus and tensile strength.
Standard atmospheric pressure is 101,325 Pa = 101.325 kPa = 1,013.25 hPa = 1,013.25 mbar = 760 torr (ISO 2533).
Meteorologists world-wide have for a long time measured air pressure in millibars. After the introduction of SI units, many preferred to preserve the customary pressure figures. Therefore, meteorologists use hectopascals today for air pressure, which are equivalent to millibars, while similar pressures are given in kilopascals in practically all other fields, where the hecto prefix is hardly ever used.
- 1 hectopascal (hPa)
- = 100 Pa = 1 mbar
- 1 kilopascal (kPa)
- = 1,000 Pa = 10 hPa
In the former Soviet mts system the unit of pressure is the pieze, which is equivalent to one kilopascal.
The Unicode computer character set has dedicated symbols ㎩ for Pa and ㎪ for kPa, but these exist merely for backwards-compatibility with some older ideographic character sets.
Examples of various values (approximately)
(See SI prefix for guide to units.)
| 0.5 Pa | Atmospheric pressure on Pluto (1988 figure; very roughly) |
| 10 Pa | Pressure increase per 1 mm of a water column¹ |
| 1 kPa | Atmospheric pressure on Mars, ∼1 % of atmospheric sea-level pressure on Earth |
| 10 kPa | Pressure increase per 1 m of a water column¹, or the drop in air pressure when going from Earth sea level to 1000 m elevation |
| 101.325 kPa | Standard atmospheric pressure for Earth sea level = 1013.25 hPa |
| 10 MPa | Pressure washers force out water at this pressure |
| 100 MPa | Pressure at bottom of Mariana Trench, about 10 km below ocean surface |
| 10 GPa | Diamond forms |
| 100 GPa | Theoretical tensile strength of carbon nanotubes (CNTs) |
¹at the Earth's surface
Comparison to other units of pressure
| 1 bar | 100,000 Pa |
| 1 millibar | 100 Pa |
| 1 atmosphere | 101,325 Pa |
| 1 mmHg (or torr) | 133.332 Pa |
| 1 inch Hg | 3,386.833 Pa |
| bar | technical/physical atmosphere | Torr | Pound-force per square inch psi | |||
|---|---|---|---|---|---|---|
| 1 Pa | ≡ 1 N/m² | = 10−5 bar | ≈ 10.2·10−6 at | ≈ 9.87·10−6 atm | ≈ 7.5·10−3 torr | ≈ 145·10−6 psi |
| 1 bar | = 100,000 Pa | ≡ 106 dyn/cm² | ≈ 1.02 at | ≈ 0.987 atm | ≈ 750 torr | ≈ 14.504 psi |
| 1 at | = 98,066.5 Pa | = 0.980665 bar | ≡ 1 kgf/cm² | ≈ 0.968 atm | ≈ 736 torr | ≈ 14.223 psi |
| 1 atm | = 101,325 Pa | = 1.01325 bar | ≈ 1.033 at | ≡ p0 | = 760 torr | ≈ 14.696 psi |
| 1 torr | ≈ 133.322 Pa | ≈ 1.333·10−3 bar | ≈ 1.360·10−3 at | ≈ 1.316·10−3 atm | ≡ 1 mmHg | ≈ 19.337·10−3 psi |
| 1 psi | ≈ 6,894.757 Pa | ≈ 68.948·10−3 bar | ≈ 70.307·10−3 at | ≈ 68.046·10−3 atm | ≈ 51.7149 torr | ≡ 1 lbf./in.² |
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