Pressure units explained

Pressure is force spread over an area, and different trades measure it in different units. This guide shows how they relate and which one to use.

Open the tool: Pressure Converter

The SI unit: the pascal

One pascal is one newton per square meter, a tiny pressure. That's why kilopascals (tires, weather), hectopascals (weather maps) and megapascals (hydraulics, material strength) are used in practice.

Where each unit is used

  • psi: tires, compressors and hydraulics in the US.
  • bar: tires, water pressure and pumps in Europe; 1 bar is close to air pressure at sea level.
  • kPa: tire placards in Canada, Japan and Australia.
  • inHg and hPa: weather and aviation.
  • mmHg: medicine, especially blood pressure.
  • inches of water: HVAC and gas appliances.

Worked example

A European car's door sticker says 2.4 bar. Multiply by 14.504: 34.8 psi, so set an American gauge to 35 psi. In kPa it is 240.