Divide by 760 for atmospheres
One standard atmosphere is exactly 760 mmHg, so the conversion is a single division. This is an exact definition, not an approximation, because both units are fixed against the pascal.
Same pressure in four units
| Pressure | mmHg | atm | kPa |
|---|---|---|---|
| Absolute vacuum | 0 | 0 | 0 |
| Diastolic blood pressure | 80 | 0.105 | 10.7 |
| Systolic blood pressure | 120 | 0.158 | 16.0 |
| Everest summit air | ~253 | ~0.33 | ~33.7 |
| Denver (1 mile up) | ~629 | 0.828 | 83.9 |
| Sea level (1 atm) | 760 | 1.000 | 101.325 |
1 atm = 760 mmHg = 101.325 kPa = 1.01325 bar = 29.92 inHg. One bar is about 750 mmHg, slightly less than an atmosphere.
To kPa and bar
- To kPa. Multiply mmHg by 0.1333. One mmHg is about 0.1333 kilopascals; one atm is 101.325 kPa.
- To bar. One atm is 1.01325 bar, so a pressure in atm and the same pressure in bar are close but not equal.
- Why medicine keeps mmHg. Blood pressure was read off mercury columns for over a century, and the unit stuck. 120/80 will not become 16/10.7 kPa any time soon.
Common questions
How many mmHg are in one atmosphere?
Exactly 760 mmHg. Since 1954 one standard atmosphere is defined as 101,325 pascals and mmHg as 101,325 divided by 760, so the 760 relationship is exact, not rounded.
Is a Torr the same as mmHg?
For any practical purpose, yes. The Torr is defined as exactly 1/760 atm and mmHg is defined slightly differently, but the two differ by less than 0.000015 percent, so they are interchangeable in the lab and the clinic.
What is blood pressure of 120 mmHg in atmospheres?
About 0.158 atm (120 divided by 760). Blood pressure is measured above atmospheric pressure, so 120/80 mmHg is roughly 0.16/0.11 atm on top of the surrounding air.
