Pressure Converter

About this Pressure Converter

The Pressure Converter changes a pressure value between common metric and imperial units. It is useful for engineering references, tire pressure comparisons, weather-related calculations and equipment specifications.

Pressure units vary widely by industry and region: meteorologists often use millibars or hectopascals, tire gauges commonly use PSI, scientific work uses pascals, and some regions use atmospheres or bar, so converting between them is routine when reading equipment specifications.

For related tasks, try Energy Converter, Power Converter or Force Converter.

How the calculation works

All values are converted through pascals as the internal base unit using fixed standard conversion factors.

How to use it

1. Enter a pressure value.
2. Choose the source unit and target unit.
3. Convert to see the equivalent pressure.

Practical example

1 bar equals 100,000 pascals and is approximately 14.5038 psi.

A car tire commonly inflated to 32 PSI converts to approximately 2.21 bar or 220,632 pascals, illustrating why tire pressure gauges calibrated in bar show noticeably smaller numbers than PSI figures.

Things to double-check

Standard atmospheric pressure at sea level is defined as exactly 101,325 pascals (1 atmosphere), a useful reference point to sanity-check a converted pressure value for a sea-level reading.

Pascals, bar, psi and atmospheres

One bar is 100 kilopascals, which is about 14.5038 psi. One standard atmosphere is 101.325 kPa, or 14.696 psi, and it is the average pressure at sea level. Weather reports often use hectopascals or millibars, where 1,013 is a normal reading. A car tyre at 32 psi is about 2.2 bar or 220 kPa. The converter makes it easy to move between these.

Tyres and everyday pressure

Tyre pressure is the pressure most people deal with. Use the figure on the placard in the door frame or the owner's manual, and check when the tyres are cold. Pressure gauges in different countries show psi, bar or kPa, so convert before you inflate. Under-inflated tyres wear faster and use more fuel, and over-inflated ones reduce grip and comfort.

Gauge and absolute pressure

Gauge pressure is measured relative to the surrounding air, and absolute pressure is measured relative to a vacuum, so absolute equals gauge plus about 101.3 kPa at sea level. A tyre gauge reading of 2.2 bar means about 3.2 bar absolute. Check which one a specification uses, since the difference is large at low pressures, and note that some instruments label gauge pressure with a g, such as psig.

Weather, health and industry

Blood pressure is given in millimetres of mercury: 120 mmHg is about 16 kPa. Weather pressure falls as altitude increases, dropping about 12 hPa for every 100 metres near sea level. Industrial equipment, such as compressors and hydraulic systems, uses bar, psi or megapascals. Always stay within the rated pressure of the equipment, and for safety-critical systems use certified gauges and follow the manufacturer's instructions.

Altitude and boiling point

Pressure changes the temperature at which water boils. At sea level, water boils at 100 degrees Celsius. At about 1,500 metres, the air pressure is near 84 kilopascals and water boils at roughly 95 degrees, and at about 3,000 metres it is closer to 90 degrees, so food takes longer to cook. A pressure cooker works the other way: at about 15 psi above atmospheric pressure, it raises the boiling point to around 121 degrees, which cooks food faster. Converting between psi, bar and kilopascals helps when you read cooker manuals and weather data.

Diving and depth

Water pressure grows quickly with depth. Every 10 metres of seawater adds roughly 1 bar, or about 100 kilopascals, to the surrounding pressure. At the surface the pressure is about 1 bar, so at 30 metres the absolute pressure is about 4 bar, which is four times the surface pressure. This is why divers must follow limits on depth and time, and why gauge pressure and absolute pressure must not be confused. Converting between bar, psi and kilopascals helps when you read cylinder gauges and dive tables from different countries.

Worked examples

A tyre inflated to 2.4 bar is about 34.8 psi. A pressure of 220 kilopascals equals 2.2 bar, or about 31.9 psi. Standard weather pressure of 1,013 hectopascals equals 101.3 kilopascals and about 14.7 psi. A blood pressure of 120 over 80 millimetres of mercury is about 16 over 10.7 kilopascals. Pressure units are many, so a clear table helps: 1 bar is 100 kilopascals, 1 psi is about 6.895 kilopascals and 1 atmosphere is 101.325 kilopascals. The converter takes care of the arithmetic.

Tyre pressure in practice

Check tyre pressure when the tyres are cold, since driving warms the air and raises the reading by a few psi. Use the value on the vehicle placard or in the manual, not the maximum printed on the tyre. Check monthly and before long trips, and adjust for heavy loads if the manufacturer advises it. Under-inflation wears the edges of the tyre and increases fuel use, while over-inflation reduces grip and wears the centre. Many modern cars have a warning system that lights up when pressure drops, but it is not a replacement for regular checks with a gauge.

Weather and altitude

Atmospheric pressure falls with altitude, by roughly 1 hectopascal for every 8 metres near sea level, which is how altimeters work. At the top of a 3,000 metre mountain, pressure is about 700 hectopascals, around 70 percent of that at sea level. Weather forecasters use pressure at sea level to compare places: falling pressure often signals approaching bad weather and rising pressure points to settled conditions. Barometers and phone sensors report pressure in hectopascals, millibars or inches of mercury, so conversion helps when you compare sources.

Industrial and household systems

Pressures vary widely in practice. Household water mains are often 3 to 5 bar, compressed air tools use about 6 to 8 bar, hydraulic equipment can run at 200 bar or more, and car engines see much higher pressures inside the cylinders. Scuba cylinders are filled to around 200 to 300 bar. Because high pressure stores a lot of energy, equipment must be rated for it and inspected regularly. Never exceed the rated pressure of a gauge, hose or vessel, and use safety valves where they are required.

Key terms explained

A pascal is one newton per square metre, and a kilopascal is a thousand pascals. A bar is 100 kilopascals, and a pound per square inch, or psi, is about 6.895 kilopascals. An atmosphere is the average pressure at sea level, 101.325 kilopascals. Gauge pressure is measured relative to the surrounding air, while absolute pressure is measured from a vacuum. A millimetre of mercury is used for blood pressure, and a hectopascal equals a millibar in weather reports.

Rules of thumb and quick checks

One bar is about 14.5 psi and about 0.987 atmospheres. To estimate psi from bar, multiply by 14.5, and to estimate bar from psi, divide by 14.5. Sea-level air pressure is about 1,013 hectopascals. Every 10 metres of water adds about one bar. Check whether a figure is gauge or absolute before you use it in a formula, and never exceed the rated pressure of a gauge, hose or vessel.

Quick reference and sanity checks

A few exact or standard values make results easy to check. One standard atmosphere is 101,325 pascals, one bar is exactly 100,000 pascals and one kilopascal is 1,000 pascals. One pound per square inch is about 6,895 pascals, and one atmosphere is about 14.7 pounds per square inch. Tyre pressures are usually gauge pressures, which measure the difference from the surrounding air, while weather and scientific values are often absolute. If a converted number is off by about 14.7 psi or 101 kPa, you have probably mixed the two. Use the unit that the equipment manual or the gauge states.

Frequently asked questions