Pressure Converter

psi stands for pounds per square inch, a unit of pressure common in tyre pressure gauges, hydraulic systems, and HVAC refrigerant measurements in the United States. One psi equals approximately 6,894.76 Pa. Typical car tyre pressures range from 30 to 35 psi.

1 atm = 101.325 kPa exactly, defined as the average atmospheric pressure at sea level on Earth. It is used as a reference for pressure measurements in diving, aviation, chemistry, and physics. One atmosphere supports a 760 mm column of mercury in a barometer.

1 bar = 100 kPa exactly. This simple decimal relationship makes conversion between bar and kPa straightforward: multiply bar by 100 to get kPa, or divide kPa by 100 to get bar. Standard atmospheric pressure is 1.01325 bar or 101.325 kPa.

mmHg (millimetres of mercury) originated from the mercury manometer invented by Evangelista Torricelli in 1643. Normal blood pressure is around 120/80 mmHg. The measurement persists due to medical convention and the vast body of clinical research and treatment guidelines that reference mmHg. Converting to kPa is straightforward: multiply mmHg by 0.133322 to get kPa.

1 atm = 14.696 psi at sea level. For everyday use, 14.7 psi is a common approximation. This value is important for understanding gauge versus absolute pressure: a tyre gauge reading of 0 psi actually measures 14.7 psi absolute because the gauge reads relative to the surrounding atmosphere.

Absolute pressure (psia) includes atmospheric pressure, while gauge pressure (psig) measures pressure relative to the atmosphere. A tyre pressure reading of 32 psi is gauge pressure, so the absolute pressure inside is about 46.7 psi at sea level. This converter uses absolute pressure in pascals as the base, so gauge readings need to be adjusted by adding atmospheric pressure (14.7 psi or 101.325 kPa) before entering the value.

Atmospheric pressure decreases with altitude exponentially. At sea level it is 1013.25 hPa (1 atm). At 1,500 m elevation it drops to about 845 hPa. At 3,000 m it is around 700 hPa. At 5,500 m (Mount Everest base camp) it is approximately 500 hPa. This affects everything from cooking times to aircraft performance to tyre pressure readings.

Normal blood pressure is around 120/80 mmHg, which equals about 16.0/10.7 kPa. The systolic (top) number measures pressure when the heart contracts, while diastolic (bottom) measures pressure between beats. Hypertension is diagnosed at readings consistently above 140/90 mmHg (18.7/12.0 kPa). Always consult a healthcare professional for interpretation.

One bar equals 100,000 Pa (exactly 100 kPa), while one standard atmosphere equals 101,325 Pa. They are close but not equal: 1 bar = 0.987 atm, and 1 atm = 1.01325 bar. The 1.325% difference matters in precision applications such as laboratory calibration, aerospace engineering, and pharmaceutical manufacturing.

Megapascal (MPa) equals 1,000,000 Pa or 1,000 kPa. It is the standard unit for material strength specifications such as steel yield strength (250 to 1,500 MPa), concrete compressive strength (20 to 40 MPa for standard mixes), and high-pressure hydraulic systems. One MPa equals approximately 145 psi.

Tyre pressure increases approximately 1 psi for every 5.5°C (10°F) temperature rise. Cold tyres (after sitting overnight) read lower than hot tyres (after highway driving). Always check and adjust tyre pressure when the tyres are cold, following the manufacturer's recommended cold pressure. Releasing air from hot tyres to reach the cold specification results in under-inflation once they cool down.

mmHg stands for millimetres of mercury, representing the height of a mercury column in a manometer or barometer. It remains in use due to medical convention for blood pressure measurement (millions of clinical studies reference mmHg), aviation altimeter settings in some countries, and vacuum measurement in laboratory equipment. One mmHg equals 133.322 Pa. The torr is essentially identical to mmHg and both units are accepted in specialised contexts.

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