How to use the pressure converter
- 1 Type the value you want to convert.
- 2 Choose the unit to convert from and the unit to convert to.
- 3 Press ⇄ to swap the two units.
- 4 Read the result, and see the same pressure in every other unit in the table below.
Tyres, pumps and weather
Tyre gauges show gauge pressure in psi or bar; weather pressure is absolute, in millibars or hectopascals. Both convert with the same factors. For temperature effects on pressure, check the Temperature Converter.
- Inflate tyres to the pressure on the door sticker, not the maximum on the tyre wall.
- 1 bar is very close to normal air pressure at sea level.
- Pressure cookers run about 1 bar above atmospheric pressure, around 15 psi.
Features
Nine pressure units
Pa, kPa, MPa, bar, mbar, psi, atm, mmHg and inHg.
Tyres and weather
psi and bar for tyres; millibar and inHg for weather.
Exact factors
1 bar = 100 kPa and 1 atm = 101.325 kPa exactly.
When to use it
Tyre pressure
Car tyres are often 30 to 35 psi, about 2.1 to 2.4 bar. Check the sticker in the door frame for your car.
Weather
Sea-level air pressure is about 1,013 mbar, or 29.92 inHg. A falling barometer often means rain.
Pumps and compressors
Water pumps and compressors may be rated in bar, psi or MPa; 10 bar is 145 psi.
Engineering and science
Convert between SI pascals and older units in data sheets. For heat and energy, see the Energy Converter.
Related Unit tasks
Frequently asked questions
How do I convert bar to psi?
Multiply by 14.5038. 2.5 bar is 36.3 psi.
How do I convert psi to bar?
Divide by 14.5038. 32 psi is 2.21 bar.
What is 1 atmosphere in psi?
14.696 psi, which is 101.325 kPa or 1.01325 bar.
What is a millibar?
One thousandth of a bar, equal to one hectopascal. Weather maps use millibars or hectopascals.
Why is blood pressure in mmHg?
Early blood pressure gauges used a column of mercury, so the unit stayed. 120 mmHg is 16 kPa.
What is the difference between gauge and absolute pressure?
Gauge pressure, as on a tyre gauge, is above the surrounding air; absolute pressure adds about 1 atmosphere.
How many kPa is 1 psi?
6.895 kPa.
What is a pascal?
The SI unit of pressure, one newton per square metre. It is very small, so kPa and MPa are more common.
How much pressure is in a gas cylinder?
Domestic LPG cylinders run at a few bar depending on temperature, while industrial gas cylinders can be 150 to 300 bar. Follow the cylinder label.
Is the result exact?
Yes for bar, atm, psi and pascals, which have exact definitions; mercury units use their standard defined values.
Why do tyre pressures change with the weather?
Air pressure in a tyre rises when it warms up and falls when it cools. Check tyres when they are cold, before driving, for the most accurate reading.
Which pressure unit do weather apps use?
Most use hectopascals or millibars, which are the same size. Some American apps use inches of mercury.
What happens if tyre pressure is too low?
Under-inflated tyres wear faster at the edges, increase fuel use and make steering less precise. Check pressure at least once a month and before long journeys.
Is higher pressure always better for pumps?
No. Pumps work best near their rated pressure. Too much pressure strains pipes and fittings, so check the rating of the whole system, not just the pump.
Which unit should engineers use?
The SI unit, the pascal, and its multiples kilopascal and megapascal are standard in engineering, although bar and psi remain common on gauges and data sheets.
Built and reviewed by Hamza Farooq, founder and lead developer
· Last updated
· How we check our tools
· Report a problem