Pressure Converter
Convert between psi, bar, atm, kPa, mmHg, and more.
Pressure measurements appear in weather forecasting, automotive maintenance, scuba diving, medical devices, and industrial engineering. The sheer number of units in common use — psi, bar, atm, Pa, kPa, mmHg, inHg, torr — reflects how different industries developed their own conventions before the SI system standardized on the pascal. Knowing how to convert between them prevents costly errors in equipment calibration and safety-critical applications.
Popular Pressure Conversions
Standards Note: Atmospheric Pressure Has a Fixed SI Anchor
NIST pressure tables fix 1 atmosphere at 101,325 pascals and about 14.6959 psi, giving you a reliable benchmark for psi, bar, kPa, and atm conversions.
The Pascal and SI Pressure Units
The pascal (Pa) is the SI unit of pressure, defined as one newton per square meter. It's a very small unit — atmospheric pressure at sea level is approximately 101,325 Pa or 101.325 kPa. In practical engineering, kilopascals (kPa) and megapascals (MPa) are more common. The bar (used widely in Europe) is exactly 100,000 Pa, making 1 bar ≈ 0.987 standard atmospheres. Most tire pressure gauges in Europe read in bar, while US gauges use psi.
Everyday Pressure Ranges
Car tire pressure typically runs 30–35 psi (2.1–2.4 bar / 207–241 kPa). Blood pressure is measured in millimeters of mercury (mmHg): normal is below 120/80 mmHg. Scuba tanks are pressurized to 200–300 bar (2,900–4,350 psi). Atmospheric pressure varies with altitude — at the summit of Mount Everest (8,849 m), pressure drops to about 33 kPa or 0.33 atm, which is why climbers need supplemental oxygen. Weather maps use hectopascals (hPa, equivalent to millibar): standard sea-level pressure is 1013.25 hPa.
| Unit / Reference | Equivalent |
|---|---|
| 1 atm (atmosphere) | 101.325 kPa / 14.696 psi / 760 mmHg |
| 1 bar | 100 kPa / 14.504 psi |
| 1 psi | 6.895 kPa / 0.0689 bar |
| 1 mmHg (torr) | 133.3 Pa / 0.0193 psi |
| 1 kPa | 0.145 psi / 0.01 bar |
| Car tire (typical) | 30–35 psi / 2.1–2.4 bar |
Tips for Accurate Pressure Measurement
Gauge pressure vs. absolute pressure is a frequent source of confusion. Gauge pressure (Pg) measures relative to atmospheric pressure; absolute pressure (Pa) includes atmospheric pressure as a baseline. A car tire at 32 psi gauge pressure is at 32 + 14.7 = 46.7 psi absolute. Tire pressure gauges read gauge pressure; vacuum gauges may read below zero (negative gauge) because they measure below atmospheric. Always clarify which reference is being used when working with pressure specifications.
Gas Pressure Unit Conversions - torr to atm, psi to atm, atm to mm Hg, kpa to mm Hg, psi to torr | The Organic Chemistry Tutor
The Organic Chemistry Tutor shows how to translate between the most common pressure units used in weather, chemistry, and engineering contexts.
Video source: The Organic Chemistry Tutor
Further Reading
Sources & References
- NIST — Units and Conversion Factors — Pressure unit conversions (PSI, bar, Pa) from NIST.