mmHg to atm Converter
Type a value in millimeters of mercury to see it in standard atmospheres as you type, with the exact formula and a reference chart.
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- Atmospheres
- 1 atm
How this was calculated
- 1 standard atmosphere = 759.9998917 millimeters of mercury
- 760 ÷ 759.9998917 = 1.0000001 atm
| mmHg | atm |
|---|---|
| 1 mmHg | 0.00131579 atm |
| 10 mmHg | 0.0131579 atm |
| 50 mmHg | 0.0657895 atm |
| 100 mmHg | 0.131579 atm |
| 120 mmHg | 0.157895 atm |
| 200 mmHg | 0.263158 atm |
| 300 mmHg | 0.394737 atm |
| 400 mmHg | 0.526316 atm |
| 500 mmHg | 0.657895 atm |
| 600 mmHg | 0.789474 atm |
| 700 mmHg | 0.921053 atm |
| 735 mmHg | 0.967105 atm |
| 750 mmHg | 0.986842 atm |
| 760 mmHg | 1 atm |
| 800 mmHg | 1.05263 atm |
| 1,000 mmHg | 1.31579 atm |
| 1,520 mmHg | 2 atm |
| atm | mmHg |
|---|---|
| 0.001 atm | 0.76 mmHg |
| 0.002 atm | 1.52 mmHg |
| 0.005 atm | 3.8 mmHg |
| 0.01 atm | 7.6 mmHg |
| 0.02 atm | 15.2 mmHg |
| 0.05 atm | 38 mmHg |
| 0.1 atm | 76 mmHg |
| 0.2 atm | 152 mmHg |
| 0.5 atm | 380 mmHg |
| 1 atm | 760 mmHg |
| 2 atm | 1,520 mmHg |
How to convert millimeters of mercury to standard atmospheres
1 millimeter of mercury = 0.0013157897 standard atmospheres. To convert millimeters of mercury to standard atmospheres, divide by 759.9998917 (or multiply by 0.0013157897). A conventional millimeter of mercury is the pressure of a 1 mm column of mercury at a fixed density and standard gravity, exactly 133.322387415 Pa, about 0.000014% more than a torr. One standard atmosphere is exactly 101,325 pascals (101.325 kPa), roughly the air pressure at sea level.
Worked examples
- 120 millimeters of mercury = 0.157895 atm (120 ÷ 759.99989)
- 760 millimeters of mercury = 1 atm (760 ÷ 759.99989)
- 1,000 millimeters of mercury = 1.31579 atm (1,000 ÷ 759.99989)
Where this conversion comes up
Millimeters of mercury are used for blood pressure, barometers and chemistry problems; standard atmospheres for chemistry, gas laws and diving. Barometers and chemistry textbooks give air pressure in millimeters of mercury; gas-law work needs atmospheres. Standard sea-level pressure is 760 mmHg, which is 1 atm. A millimeter of mercury and a torr differ by less than one part in seven million, so for any practical answer mmHg and torr are interchangeable. Blood pressure (120/80 mmHg) is gauge pressure above the surrounding air, so 120 mmHg is 0.158 atm above atmospheric, not an absolute pressure.
Quick estimate
Divide by 760: 380 mmHg ≈ 0.5 atm.
Common mistakes
- Multiplying instead of dividing. A standard atmosphere is larger than a millimeter of mercury, so the number of standard atmospheres must come out smaller: 120 millimeters of mercury = 0.157895 atm.
- Rounding too early. Keep the full factor until the last step; rounding 0.00132 to 0.0013 first puts large values noticeably off.
Related pressure converters: bar to psi, psi to bar, kpa to psi, psi to kpa, mpa to psi, psi to mpa.
Frequently asked questions
How do you convert millimeters of mercury to standard atmospheres?
Multiply the millimeters of mercury by 0.0013157897 (or divide by 759.9998917). For example, 760 millimeters of mercury is 1 standard atmospheres.
How many standard atmospheres are in one millimeter of mercury?
One millimeter of mercury is 0.0013157897 standard atmospheres. A conventional millimeter of mercury is the pressure of a 1 mm column of mercury at a fixed density and standard gravity, exactly 133.322387415 Pa, about 0.000014% more than a torr.
What is 1,000 millimeters of mercury in standard atmospheres?
1,000 millimeters of mercury is 1.31579 standard atmospheres.
Is there a quick way to estimate millimeters of mercury to standard atmospheres?
Divide by 760: 380 mmHg ≈ 0.5 atm.