Pressure Conversion
Convert pressure conversion between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Pressure Conversion
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Formula: Target = Value x (Source-to-Pa factor) / (Target-to-Pa factor)
Worked example — 2.4 bar = 34.81 PSI = 240 kPa = 2.37 atm
Formula
Target = Value x (Source-to-Pa factor) / (Target-to-Pa factor)
All conversions go through pascals as the common base unit. First multiply the input value by its unit factor to get pascals, then divide by the target unit factor. For example, 1 atm = 1 x 101325 Pa, then to PSI: 101325 / 6894.76 = 14.696 PSI.
Worked Examples
Example 1: Converting Tire Pressure Units
Problem:Convert 2.4 bar to PSI, kPa, and atm.
Solution:Pa = 2.4 x 100000 = 240000 Pa PSI = 240000 / 6894.76 = 34.809 PSI kPa = 240000 / 1000 = 240.000 kPa atm = 240000 / 101325 = 2.369 atm
Result:2.4 bar = 34.81 PSI = 240 kPa = 2.37 atm
Example 2: Medical Blood Pressure Conversion
Problem:A systolic reading of 120 mmHg. What is this in kPa and PSI?
Solution:Pa = 120 x 133.322 = 15998.64 Pa kPa = 15998.64 / 1000 = 15.999 kPa PSI = 15998.64 / 6894.76 = 2.320 PSI atm = 15998.64 / 101325 = 0.158 atm
Result:120 mmHg = 16.00 kPa = 2.32 PSI
Frequently Asked Questions
What are the most common pressure units and how do they relate?
The most common pressure units are pascal (Pa), bar, atmosphere (atm), PSI, torr, and mmHg. One standard atmosphere equals 101,325 Pa, 1.01325 bar, 14.696 PSI, 760 torr, and 760 mmHg. The pascal is the SI unit (1 N/m2), while bar is popular in European industrial settings. PSI dominates in American engineering. Torr and mmHg are used in vacuum science and medicine respectively. Each unit emerged from different fields, which is why so many coexist in modern use.
Why are there so many different pressure units?
Different pressure units developed independently across various fields and countries. The pascal came from the SI system in 1971. The atmosphere was defined by the pressure at sea level. The torr originated from mercury barometer measurements in the 1600s. PSI developed from the imperial system used in America and Britain. The bar was created as a convenient metric unit close to atmospheric pressure. Each field adopted the unit most convenient for its typical pressure ranges, and legacy usage keeps them all in active use today.
What is gauge pressure versus absolute pressure?
Absolute pressure measures from a perfect vacuum (zero point), while gauge pressure measures relative to the local atmospheric pressure. At sea level, atmospheric pressure is about 101.325 kPa (14.696 PSI), so a tire gauge reading 32 PSI (gauge) actually means 46.7 PSI absolute. Gauge pressure can be negative (vacuum), while absolute pressure is always positive. Units are sometimes suffixed with "a" for absolute (psia) or "g" for gauge (psig). Scientific calculations typically require absolute pressure.
How do I choose the right pressure unit for my application?
Use pascals or kilopascals for scientific work and international standards. Use bar for European industrial applications and meteorology (as hectopascals). Use PSI for American automotive, HVAC, and industrial applications. Use torr or millitorr for vacuum science and semiconductor manufacturing. Use mmHg for blood pressure and medical applications. Use atmospheres for chemistry and diving calculations. When in doubt, the pascal is always correct as the SI unit, and any other unit can be derived from it.
How is the pascal defined in SI base units?
One pascal is one newton per square metre. Expanding the newton into base units gives 1 Pa = 1 kg/(m s^2), so pressure carries dimensions of mass divided by length and time squared. Every other pressure unit on this converter is a fixed multiple of that quantity, which is why routing all conversions through pascals guarantees dimensional consistency however unusual the source and target units are.
How do I convert a manometer reading in mmHg or inches of water to pascals?
These units express pressure as the height of a liquid column. One millimetre of mercury, also called a torr, is 133.322 pascals, and one inch of water at 4 degrees Celsius is about 249.089 pascals. Because both depend on the fluid's density and on local gravity, the published factors assume a standard density and standard gravity, and precise work applies a temperature correction to the column fluid.
What is the difference between the bar, the standard atmosphere and the technical atmosphere?
The bar is defined as exactly 100,000 pascals, a round metric figure. The standard atmosphere is exactly 101,325 pascals, historically tied to mean sea-level pressure, so it is about 1.3 percent larger than a bar. The technical atmosphere, one kilogram-force per square centimetre, is 98,066.5 pascals. All three are close enough to be confused and far enough apart to matter in calibration, so the symbol should always be stated.
How does a column of fluid turn height into pressure?
Hydrostatic pressure is p = rho g h, the fluid density times gravitational acceleration times the vertical height of the column. Ten metres of fresh water at about 998 kg/m3 gives 998 x 9.81 x 10 = 97,900 pascals, close to one bar. Mercury is roughly 13.6 times denser and produces the same pressure in about 736 millimetres, which is why barometers were built with mercury rather than water.
Why do vacuum systems use torr and millibar?
Vacuum work spans many orders of magnitude below atmospheric pressure, and torr and millibar keep the interesting range readable: rough vacuum around 1 to 100 torr, high vacuum near 10^-6 torr. The torr survives from mercury manometry while the millibar is common in European instrumentation. Both are simply scaled pascals, so conversion is one multiplication, though gauge calibration itself is gas dependent at low pressure.
What do psia, psig and psid mean?
Psia is pressure measured against a perfect vacuum, psig is measured against the surrounding atmosphere, and psid is a differential between two points. At sea level psia is about 14.696 higher than psig for the same condition. A unit conversion preserves whichever reference the original reading used, so converting 30 psig to bar gives 2.07 bar gauge, not absolute; add local atmospheric pressure first if an absolute value is needed.
References
Background & Theory
1 atmosphere = 101,325 Pa = 1.01325 bar = 760 torr = 14.6959488 psi. The pascal, one newton per square metre, is the coherent SI unit, and every other pressure unit on this page is defined against it.
Conversion reference table
| Conversion | Equivalent | Exact or rounded? |
|---|---|---|
| 1 pascal | 1 newton per square metre | Exact by definition |
| 1 bar | 100,000 pascals | Exact by definition |
| 1 standard atmosphere | 101,325 pascals | Exact by definition |
| 1 psi | 6,894.75729317 pascals | Exact by definition |
| 1 torr | 101325/760 = 133.322368 pascals | Exact fraction |
| 1 mmHg (conventional) | 133.322387415 pascals | Exact by convention |
| 1 inch of mercury | 3,386.389 pascals | Defined, rounded |
| 1 metre of water (4 C) | 9,806.65 pascals | Conventional |
Always establish the reference before converting: gauge pressure is measured against the surrounding atmosphere, absolute pressure against a vacuum, and differential pressure between two points. A tyre gauge reading 32 psig is 46.7 psia at sea level, and mixing the two is the most common error in pressure work. Meteorology adds a further step by reducing station readings to sea level, which is why an airport at altitude reports a pressure far higher than a barometer there actually measures.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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