1 mmHg = 0.00131579 atm (millimeter of mercury → standard atmosphere)
1 mmHg = 0.00131579 atm
1 millimeter of mercury equals 0.00131579 standard atmospheres. To convert millimeters of mercury to standard atmospheres, multiply the millimeter of mercury value by 0.00131579. For quick reference: 1 mmHg = 0.00131579 atm, 5 mmHg = 0.00657895 atm, 10 mmHg = 0.0131579 atm, 100 mmHg = 0.131579 atm.
Standard atmospheres = Millimeters of mercury × 0.00131579Millimetres of mercury to standard atmospheres divides by about 760 (101,325 ÷ 133.322387415 = 759.9998 mmHg per atm). A 380 mmHg partial-pressure figure is 0.5 atm; a barometer at 745 mmHg reads 0.980 atm. Chemistry gas-law work and altitude physiology both use this pairing — oxygen partial pressures at elevation are classically tabulated in mmHg against atm references. The mmHg and the torr (exactly 1/760 atm) are nearly identical but not the same unit; only in high-precision vacuum work does the distinction surface.
Hyperbaric-chamber protocols sometimes record chamber pressure in millimetres of mercury from legacy manometers, then express the reading as a fraction of a standard atmosphere for patient charts. A reading of 380 mmHg is exactly 0.500 atm, half of sea-level pressure and roughly equivalent to 5,500 m altitude; 570 mmHg is 0.750 atm. Because 1 atm was historically defined as 760 mmHg, this conversion is exact rather than approximate, which is why hyperbaric medicine still tolerates mmHg readings even in an otherwise SI-standardised clinical setting.
Start with your value in millimeters of mercury.
Multiply the millimeter of mercury value by 0.00131579. This is the exact conversion factor from millimeters of mercury to standard atmospheres.
The product is your value in standard atmospheres. For example, 5 mmHg × 0.00131579 = 0.00657895 atm.
The exact factor from millimeters of mercury to standard atmospheres is 0.00131579.
Standard atmospheres = Millimeters of mercury × 0.00131579
Fifty common reference values, hand-picked for skim utility. Use the calculator above for any value not listed.
| Millimeters of mercury (mmHg) | Standard atmospheres (atm) |
|---|---|
| 0.001 mmHg | 1.3158 × 10^−6 atm |
| 0.01 mmHg | 1.3158 × 10^−5 atm |
| 0.1 mmHg | 0.00013158 atm |
| 0.5 mmHg | 0.00065789 atm |
| 1 mmHg | 0.0013158 atm |
| 1.5 mmHg | 0.0019737 atm |
| 2 mmHg | 0.0026316 atm |
| 2.5 mmHg | 0.0032895 atm |
| 3 mmHg | 0.0039474 atm |
| 4 mmHg | 0.0052632 atm |
| 5 mmHg | 0.0065789 atm |
| 6 mmHg | 0.0078947 atm |
| 7 mmHg | 0.0092105 atm |
| 8 mmHg | 0.010526 atm |
| 9 mmHg | 0.011842 atm |
| 10 mmHg | 0.013158 atm |
| 14 mmHg | 0.018421 atm |
| 15 mmHg | 0.019737 atm |
| 20 mmHg | 0.026316 atm |
| 25 mmHg | 0.032895 atm |
| 30 mmHg | 0.039474 atm |
| 32 mmHg | 0.042105 atm |
| 35 mmHg | 0.046053 atm |
| 40 mmHg | 0.052632 atm |
| 50 mmHg | 0.065789 atm |
| 60 mmHg | 0.078947 atm |
| 75 mmHg | 0.098684 atm |
| 80 mmHg | 0.10526 atm |
| 100 mmHg | 0.13158 atm |
| 101.325 mmHg | 0.13332 atm |
| 150 mmHg | 0.19737 atm |
| 200 mmHg | 0.26316 atm |
| 250 mmHg | 0.32895 atm |
| 300 mmHg | 0.39474 atm |
| 400 mmHg | 0.52632 atm |
| 500 mmHg | 0.65789 atm |
| 760 mmHg | 1 atm |
| 1000 mmHg | 1.3158 atm |
| 1013.25 mmHg | 1.3332 atm |
| 2000 mmHg | 2.6316 atm |
| 5000 mmHg | 6.5789 atm |
| 10000 mmHg | 13.158 atm |
| 14.7 mmHg | 0.019342 atm |
| 50000 mmHg | 65.789 atm |
| 100000 mmHg | 131.58 atm |
| 101325 mmHg | 133.32 atm |
| 200000 mmHg | 263.16 atm |
| 500000 mmHg | 657.89 atm |
| 1000000 mmHg | 1315.8 atm |
| 10000000 mmHg | 13158 atm |
Normal blood pressure is around 120/80 mmHg. Atmospheric pressure at sea level is roughly 760 mmHg.
The millimeter of mercury (mmHg) equals approximately 133.322 Pa — the pressure exerted by a 1 mm column of mercury under standard gravity. It is the conventional unit for blood pressure worldwide, even in countries that have otherwise gone fully metric.
The standard atmosphere (atm) is defined as exactly 101,325 Pa. It is the conventional reference for chemistry (gas-law calculations), aviation altimetry, and historic engineering. Despite the name, it is not the actual atmospheric pressure at any single place — that varies daily.
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