mmHg to Atmospheres Converter
Unit ConversionConvert millimeters of mercury to standard atmospheres. 1 millimeter of mercury is about 0.00131579 standard atmospheres, with a conversion table and the reverse conversion.
Atmospheres
Equivalent pressure in standard atmospheres
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SponsoredThis converter turns millimeters of mercury into standard atmospheres (mmHg to atm). Enter a value and the result updates as you type. 1 millimeter of mercury is about 0.00131579 standard atmospheres.
1 millimeter of mercury is exactly 133.322387415 pascals, the conventional value based on mercury density and standard gravity. 1 standard atmosphere is exactly 101,325 pascals, a reference value close to average sea-level air pressure. That puts 760 mmHg very slightly above one atmosphere.
The result shows 0 for a negative entry, because absolute pressure, counted from a perfect vacuum, cannot be negative. The result is rounded to 6 decimal places.
How to Convert mmHg to Atmospheres
To convert millimeters of mercury to standard atmospheres, multiply by 133.322387415 and divide by 101,325. For example, 750 mmHg is about 0.986842 atm.
To go from standard atmospheres back to millimeters of mercury, multiply atmospheres by about 759.99989.
mmHg to Atmospheres Conversion Table
Common mmHg values converted to standard atmospheres, rounded to 6 decimal places.
| mmHg | Atmospheres |
|---|---|
| 1 mmHg | 0.001316 atm |
| 100 mmHg | 0.131579 atm |
| 250 mmHg | 0.328947 atm |
| 400 mmHg | 0.526316 atm |
| 500 mmHg | 0.657895 atm |
| 700 mmHg | 0.921053 atm |
| 750 mmHg | 0.986842 atm |
| 760 mmHg | 1 atm |
| 800 mmHg | 1.052632 atm |
| 1,000 mmHg | 1.31579 atm |
| 1,520 mmHg | 2 atm |
| 7,600 mmHg | 10.000001 atm |
mmHg, Torr and the Atmosphere
760 mmHg is often called one atmosphere, but that is exactly true only for the torr: 760 torr equals exactly 1 atm. The conventional millimeter of mercury is defined separately, so 760 mmHg is about 1.00000014 atm and 1 atm is about 759.99989 mmHg. The gap is under one part in a million, according to the factors in the IUPAC Green Book. Chemistry classes usually use 760 mmHg for 1 atm, which is fine at the precision of class problems.
mmHg is the usual unit for blood pressure, as in the Mean Arterial Pressure Calculator. For weather, NOAA reports pressure in inches of mercury and millibars. Gas calculations take atmospheres, the input unit of the Ideal Gas Law Calculator.
Frequently Asked Questions
How many mmHg is 1 atm?
1 atm is about 759.99989 mmHg, usually rounded to 760 mmHg.
Is 760 mmHg exactly 1 atm?
Not quite. 760 torr is exactly 1 atm, but 760 mmHg is about 1.00000014 atm, because the conventional mmHg is very slightly larger than the torr.
How do I convert atm to mmHg?
Multiply atmospheres by about 759.99989, or by 760 for most practical purposes.
Is the mmHg to Atmospheres factor exact?
The factor is fixed by definitions, so it never changes, but it has no finite decimal form. 1 millimeter of mercury is about 0.00131579 standard atmospheres. The calculator uses the full value and rounds only the result it shows.
What happens if I enter a negative value?
It shows 0. Both values are treated as absolute pressures here, which cannot be negative.
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