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Units of pressure
Beginner
Pascal, atmosphere, bar and mmHg.
Key relation
1 atm = 1.013×10⁵ PaThe pascal (N/m²), atmosphere (101,325 Pa), bar (10⁵ Pa), mmHg or torr (133.3 Pa) and psi (6895 Pa).
Worked example
Tyre at 32 psi ≈ 220 kPa.
Common mistake
Gauge vs absolute pressure differ by one atmosphere.
In more detail
Pressure is measured in pascals, bar, atmospheres and millimetres of mercury. One atmosphere is about 101,325 Pa, and one bar is 100,000 Pa.
Real-world uses
- Weather reports quote pressure in hectopascals or millibars.
- Medical blood pressure is measured in millimetres of mercury.
- Weather reports use hectopascals, while tyre pressures are often given in bar or pounds per square inch.
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Frequently asked questions
How many pascals is one atmosphere?
About 101,325 Pa.
Why is blood pressure in mmHg?
Historically, mercury manometers were used to measure it, and the unit remains standard.
How many pascals is one atmosphere?
About 101 325 pascals, or roughly 100 kilopascals.
Related topics in Fluids & Elasticity
Density · Relative density · Pressure · Pressure in a fluid · Pascal's law · Hydraulic press