Converters

Pressure Converter

Convert any pressure value between Pascal, kilopascal, megapascal, bar, PSI, atmosphere, mmHg, and inHg. All units shown at once.

Enter a value and select a unit to convert all pressure units at once.

Advertisement

Pressure Conversion Reference

All conversions use the Pascal (Pa) as the base unit. Multiply by the factor below to convert to Pa.

1 kPa = 1,000 Pa

1 MPa = 1,000,000 Pa

1 bar = 100,000 Pa

1 PSI = 6,894.757 Pa

1 atm = 101,325 Pa

1 mmHg = 133.322 Pa

1 inHg = 3,386.389 Pa

Pressure in Science and Engineering

Pressure is defined as force per unit area: P = F/A. The SI unit is the Pascal (Pa), named after Blaise Pascal, equal to one Newton per square metre. Because the Pascal is a very small unit for most practical purposes, kilopascals (kPa) and megapascals (MPa) are commonly used in engineering.

In fluid mechanics, pressure plays a central role. Pascal's law states that pressure applied to a confined fluid is transmitted equally in all directions. This principle underlies hydraulic systems in vehicles, construction equipment, and industrial machinery. The pressure at a depth h in a fluid of density ρ is P = ρgh, where g is gravitational acceleration.

In meteorology, atmospheric pressure is measured by barometers and reported in hectopascals (hPa, identical to millibar). Falling pressure typically indicates approaching storms; rising pressure indicates clearing weather. The Beaufort wind scale and weather forecasting rely heavily on barometric pressure trends.

Frequently asked questions

What are the most common pressure units?
The most common pressure units are the Pascal (Pa), the SI base unit; kilopascal (kPa, 1000 Pa); megapascal (MPa, 1,000,000 Pa); bar (100,000 Pa); PSI (pounds per square inch, used in the US for tyres and gas pressure); atmosphere (atm, approximately 101,325 Pa representing standard atmospheric pressure at sea level); and mmHg (millimetres of mercury, also called Torr), which is used extensively in medical contexts for blood pressure measurement.
How do you convert PSI to bar?
To convert PSI to bar, multiply by approximately 0.0689. One PSI equals 6,894.757 Pascals, and one bar equals 100,000 Pascals. Therefore 1 PSI = 6894.757 / 100000 ≈ 0.06895 bar. Conversely, to convert bar to PSI, multiply by approximately 14.504. For example, a tyre inflated to 2.5 bar is approximately 36.3 PSI.
What is the difference between gauge pressure and absolute pressure?
Absolute pressure is measured relative to a perfect vacuum (zero pressure). Gauge pressure is measured relative to atmospheric pressure — it is the pressure above or below atmospheric. Standard atmospheric pressure is approximately 101,325 Pa or 14.696 PSI. A tyre inflated to 35 PSI gauge pressure has an absolute pressure of about 35 + 14.7 = 49.7 PSI absolute. Most everyday pressure gauges measure gauge pressure; scientific instruments often use absolute pressure. When converting between pressure units, ensure you are comparing the same reference baseline.
Why is mmHg used for blood pressure?
Mercury manometers were the original instruments used to measure blood pressure clinically. The height of a mercury column supported by the blood pressure was recorded in millimetres, giving the mmHg unit. Even though modern blood pressure cuffs use electronic sensors rather than mercury, the mmHg unit has been retained for historical continuity and standardisation across medical practice worldwide. Standard resting blood pressure is around 120/80 mmHg.
What is atmospheric pressure and why does it change with altitude?
Standard atmospheric pressure at sea level is defined as 101,325 Pa (1 atm, 1013.25 hPa, or 14.696 PSI). It represents the weight of the column of air above a unit area of Earth's surface. As altitude increases, there is less air above you, so atmospheric pressure decreases. At 5,500 metres elevation, atmospheric pressure is roughly half of sea level pressure. This is why aeroplane cabins are pressurised, why water boils at lower temperatures at altitude, and why weather is partially described by barometric pressure readings.
What is a bar of pressure and where is it used?
The bar is a non-SI unit of pressure equal to 100,000 Pascals, approximately equal to atmospheric pressure at sea level. It is widely used in meteorology, where pressure is often reported in millibars (mbar or hPa, both equal to 100 Pa). Scuba diving equipment uses bar for tank pressure ratings. Industrial pneumatic systems in Europe typically use bar. It is also used in food processing, hydraulic engineering, and chemical manufacturing.

Related calculators