🌡️ Pressure Conversion Guide
Complete pressure conversion guide — psi, bar, atmospheres, kilopascals, mmHg, inHg, torr. For tires, plumbing, scuba diving, and weather.
Pressure is force divided by area. It has the most competing units of any measurement — psi in the US, bar in Europe, pascals for science, mmHg for medicine, millibars for weather.
Why so many pressure units?
- Pascal (Pa) — SI unit, N/m^2. Tiny — three apples on a 1 m^2 table.
- Bar — 100,000 Pa exactly. Almost equals 1 atm.
- PSI — US standard for tires, plumbing, industrial pressure.
- Atmosphere (atm) — 101,325 Pa, average sea-level pressure at 15 C.
- mmHg — from 17th-century mercury barometers. 760 mmHg = 1 atm.
Gauge vs absolute pressure
Most gauges read pressure above atmospheric. Absolute = gauge + 1 atm. A bike tire at 100 psi gauge = 100 + 14.7 = 114.7 psi absolute.
Scuba diving
Every 10 meters adds approximately 1 bar. At 30 m, 4 bar absolute. Your regulator delivers air at ambient pressure. Nitrogen narcosis starts below about 30 meters.
Plumbing and water pressure
Municipal systems deliver 2-4 bar (29-58 psi). A 5-story building needs 40-50 m of water head = 4-5 bar at the top floor.
Related converters
Frequently asked questions
What is 1 atm in psi?
1 atm = 14.696 psi = 1.01325 bar = 101.325 kPa = 760 mmHg. Standard sea-level atmospheric pressure.
Is bar more accurate than atm?
Both are defined constants. bar = 100,000 Pa exactly. atm = 101,325 Pa. They differ by about 1.3%.
How do I convert mmHg to kPa?
1 mmHg = 0.133322 kPa. 120 mmHg (systolic BP) = 16.0 kPa.
Why do scuba divers use bar?
Because 1 bar = 10 meters of water depth. 30 m = 3 bar gauge + 1 atm surface = 4 bar absolute.
Last updated — conversions use exact ISO unit definitions.