Pressure Converter

These are three common pressure units from different systems. Pascal (Pa): The SI base unit. 1 Pa = 1 N/m² (one newton per square meter). Very small — atmospheric pressure is about 101,325 Pa. Bar: Metric unit. 1 bar = 100,000 Pa. Very close to 1 atmosphere. Common in European engineering and meteorology. PSI (Pounds per Square Inch): Imperial unit used in the US. 1 PSI = 6,894.76 Pa. Common in tire pressure, hydraulics, plumbing. Conversions: 1 bar = 14.5038 PSI = 100,000 Pa. 1 atmosphere (atm) = 1.01325 bar = 14.696 PSI. For everyday US use: tire pressure (32 PSI ≈ 2.2 bar), blood pressure (120/80 mmHg ≈ 16/11 kPa).

Standard atmospheric pressure at sea level: 1 atm = 101,325 Pa = 1013.25 hPa (millibar) = 14.696 PSI = 760 mmHg = 29.92 inHg. Altitude effects: At 1,000m: ~898 hPa (11% lower). At 3,000m (Denver, CO): ~701 hPa (31% lower). At 8,849m (Everest summit): ~314 hPa (69% lower). Weather forecasting: High pressure (>1013 hPa) = clear/fair weather. Low pressure (<1013 hPa) = clouds/rain. Pressure drops ~12 hPa per 100m gain in elevation (roughly). Barometric pressure is typically expressed in hPa (= millibar) or inHg in aviation/weather.

Absolute pressure: Pressure measured relative to a perfect vacuum (0 pressure). Gauge pressure: Pressure measured relative to atmospheric pressure. Gauge pressure = Absolute pressure − Atmospheric pressure. Examples: A car tire inflated to 32 PSI gauge = 32 + 14.7 = 46.7 PSI absolute. A tire at 0 PSI gauge is not flat — it still has atmospheric pressure (14.7 PSI absolute). Blood pressure: 120/80 mmHg is gauge pressure (above atmospheric). Vacuum: Negative gauge pressure. Full vacuum = −14.7 PSI gauge = 0 PSI absolute. This calculator uses absolute pressure. When working with tires or hydraulics, remember to add atmospheric pressure if using gauge readings.

mmHg (millimeters of mercury) originated from mercury manometers — tube instruments where pressure was measured by how high it could push a column of mercury. 1 mmHg = 133.322 Pa = 0.0193 PSI. Also called Torr (1 Torr ≈ 1 mmHg, exact: 1 atm = 760 Torr). Still used in: Medicine: Blood pressure (e.g., 120/80 mmHg), intraocular pressure. Vacuum technology: Describing low-pressure environments. Meteorology (older equipment). Barometric pressure in US weather: often shown as inHg (inches of mercury). 1 inHg = 25.4 mmHg = 3,386.4 Pa. Standard atmosphere = 29.92 inHg = 760 mmHg.

Everyday applications: Tire pressure: PSI (US), bar (Europe). Blood pressure: mmHg (worldwide). Weather/barometric: hPa / millibar (meteorology), inHg (US aviation/weather). Bicycle tires: PSI or bar. Engineering applications: Hydraulics: PSI (US), bar or MPa (metric). Compressed air systems: PSI or bar. Water supply: PSI (US), kPa or bar (metric). Structural loads: kPa or MPa. Vacuum systems: Torr, Pa, mbar. High-pressure research: GPa (gigapascal). Food safety (sterilization): bar or PSI. The SI system uses Pascal and its multiples (kPa, MPa, GPa) for all scientific work.