How to Convert Millimetres of mercury to Atmospheres (mmHg to atm)
Pressure conversions are used for tyre pressure (psi or bar), blood pressure readings in mmHg and weather maps in millibars. This guide shows how to convert millimetres of mercury into atmospheres by hand, with examples and a quick-reference table.
The conversion
To convert millimetres of mercury to atmospheres, multiply the value by 0.0013157858. To go the other way, divide by the same number (or multiply by 760.0021001785). For a quick estimate, multiply by about 0.0013.
Atmospheres = millimetres of mercury × 0.0013157858
Worked examples
- 3 mmHg = 0.003947 atm
- 12.5 mmHg = 0.016447 atm
- 75 mmHg = 0.098684 atm
Millimetres of mercury to Atmospheres table
| Millimetres of mercury | Atmospheres |
|---|---|
| 1 mmHg | 0.001316 atm |
| 2 mmHg | 0.002632 atm |
| 5 mmHg | 0.006579 atm |
| 10 mmHg | 0.013158 atm |
| 20 mmHg | 0.026316 atm |
| 25 mmHg | 0.032895 atm |
| 50 mmHg | 0.065789 atm |
| 100 mmHg | 0.131579 atm |
| 250 mmHg | 0.328946 atm |
| 500 mmHg | 0.657893 atm |
| 1,000 mmHg | 1.3158 atm |
Common questions
Is mmHg to atm exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Atmospheres to Millimetres of mercury converter.
Mistakes to avoid
Forgetting squared and cubed units
Area and volume factors are the length factor squared or cubed, so 1 m² is about 10.76 sq ft, not 3.28.
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
Multiplying when you should divide
Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.
Background
Singapore adopted the metric system in the 1970s, replacing imperial units and traditional Chinese measures in most official uses. Metric units are now standard in schools, trade and government, but older units survive in property, markets and imported goods.
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
For any value, use the Millimetres of mercury to Atmospheres Converter or browse all pressure converters.
Run your own numbers: Millimetres of mercury to Atmospheres Converter