ATM Pressure Conversion Calculator
Enter a pressure value in any unit and this calculator converts it instantly to all eight other pressure units. Switch between atmospheres, PSI, pascals, kilopascals, bar, millibar, torr, mmHg, and inches of mercury. All conversions use the exact SI definition of the standard atmosphere (1 atm = 101,325 Pa).
Formula
Worked example
Convert 2.5 atm to PSI and kPa. PSI: 2.5 x 14.6959 = 36.74 PSI. kPa: 2.5 x 101.325 = 253.31 kPa. Reverse: 36.74 PSI / 14.6959 = 2.5 atm.
What is an atmosphere (atm)?
The standard atmosphere (symbol: atm) is a unit of pressure defined by the International Union of Pure and Applied Chemistry as exactly 101,325 pascals (Pa). It was originally set to approximate the mean air pressure at sea level on Earth. Today it is used as a convenient reference point in science and engineering, even though it is not part of the SI system. The modern SI unit for pressure is the pascal, but the atmosphere remains widely used in chemistry (particularly for gas laws), meteorology, and everyday descriptions of pressure.
How to convert between pressure units
Every pressure conversion is a multiplication by a fixed factor. To convert from atmospheres to another unit, multiply by the factor shown in the reference table. To convert any unit back to atmospheres, divide by that same factor. For example, to convert 3 atm to PSI: 3 x 14.6959 = 44.09 PSI. To go the other direction, 44.09 PSI / 14.6959 = 3 atm. This calculator accepts any of the nine supported units as input and computes the remaining eight simultaneously, so there is no need to chain conversions.
Pressure units in everyday use
Different fields have adopted different pressure units. Meteorologists in Europe report air pressure in hectopascals (hPa) or millibars (mbar), while the US National Weather Service uses inches of mercury (inHg). Doctors measure blood pressure in millimetres of mercury (mmHg); a typical healthy reading of 120/80 mmHg equals about 16 kPa. Tyre pressure is reported in PSI in North America and bar across most of Europe. The pascal is the standard in scientific literature. Torr appears frequently in vacuum science and laboratory work. Understanding which unit applies in your context prevents costly conversion mistakes.
Torr and mmHg: are they the same?
For practical purposes, 1 Torr equals 1 mmHg. The Torr was originally defined as the pressure of exactly 1 mm of mercury at 0 degrees Celsius under standard gravity. A later precise definition set 1 Torr = 101,325 / 760 Pa, making it differ from 1 mmHg by less than 0.000016 percent. In any engineering, medical, or laboratory context this difference is negligible, and the two units are treated as identical.
Common pressure values in all units
| Description | atm | PSI | kPa | bar | mmHg |
|---|---|---|---|---|---|
| Standard atmosphere | 1.000 | 14.70 | 101.33 | 1.013 | 760.0 |
| Tyre pressure (car, typical) | 2.040 | 30.0 | 206.8 | 2.068 | 1551 |
| Sea-level min (storms) | 0.960 | 14.10 | 97.0 | 0.970 | 727.5 |
| 5,000 m elevation | 0.533 | 7.83 | 54.0 | 0.540 | 405.0 |
| Diver at 10 m depth | 2.000 | 29.40 | 202.7 | 2.027 | 1520 |
| Bicycle tyre (road) | 5.100 | 75.0 | 517.1 | 5.171 | 3858 |
| Normal blood pressure (sys) | 0.158 | 2.32 | 16.0 | 0.160 | 120.0 |
| Vacuum (near-zero) | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
Reference values for frequently encountered pressures, converted across all supported units.
Frequently asked questions
How many PSI is 1 atm?
1 standard atmosphere equals exactly 14.695948775 PSI. In practice, this is rounded to 14.696 PSI or 14.7 PSI. To convert any atm value to PSI, multiply by 14.696. To go from PSI back to atm, divide by 14.696.
How many pascals is 1 atm?
1 standard atmosphere is defined as exactly 101,325 pascals. This is the exact SI definition, so there is no rounding involved. 1 atm = 101,325 Pa = 101.325 kPa.
What is the difference between atm and bar?
1 atm = 1.01325 bar, or equivalently 1 bar = 0.986923 atm. They are very close but not identical. The bar was defined as 100,000 Pa (100 kPa) to be a round number close to one atmosphere. For many practical purposes the two can be used interchangeably with less than 1.4 percent error, but for precise science or engineering calculations use the exact factors.
Why is mmHg used for blood pressure?
Early sphygmomanometers (blood pressure devices) used a column of mercury as the pressure indicator, so readings were recorded as the height of mercury in millimetres. The unit stuck in medicine even after mercury instruments were replaced by electronic ones. A normal systolic blood pressure of 120 mmHg equals about 0.158 atm or 16 kPa.
How do I convert kPa to atm?
Divide the kPa value by 101.325. For example, 202.65 kPa / 101.325 = 2.0 atm. Conversely, to convert atm to kPa, multiply by 101.325.
What pressure is 1 atm in everyday terms?
1 atm is the approximate air pressure pressing down on your body at sea level. It equals 14.696 PSI, 101.325 kPa, 1.01325 bar, 760 mmHg, and 29.92 inHg. A typical car tyre is inflated to about 2 atm above atmospheric pressure (called gauge pressure), so the absolute pressure inside the tyre is about 3 atm.