How to Convert PSI to Millimetres of mercury (psi to mmHg)
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 psi into millimetres of mercury by hand, with examples and a quick-reference table.
The conversion
To convert psi to millimetres of mercury, multiply the value by 51.7150732812. To go the other way, divide by the same number (or multiply by 0.0193367221). For a quick estimate, multiply by about 52.
Millimetres of mercury = psi × 51.7150732812
Worked examples
- 3 psi = 155.1452 mmHg
- 12.5 psi = 646.4384 mmHg
- 75 psi = 3,878.63 mmHg
PSI to Millimetres of mercury table
| PSI | Millimetres of mercury |
|---|---|
| 1 psi | 51.7151 mmHg |
| 2 psi | 103.4301 mmHg |
| 5 psi | 258.5754 mmHg |
| 10 psi | 517.1507 mmHg |
| 20 psi | 1,034.3 mmHg |
| 25 psi | 1,292.88 mmHg |
| 50 psi | 2,585.75 mmHg |
| 100 psi | 5,171.51 mmHg |
| 250 psi | 12,928.77 mmHg |
| 500 psi | 25,857.54 mmHg |
| 1,000 psi | 51,715.07 mmHg |
Common questions
Is psi to mmHg 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 Millimetres of mercury to PSI converter.
Mistakes to avoid
Rounding the factor too early
Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.
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.
Background
For everyday use, three or four significant figures are usually enough. Engineering, science and trade documents may need more, and rounding should happen only at the end of a calculation.
Many conversion factors are exact by definition. The inch has been defined as exactly 2.54 centimetres since 1959, and the pound as exactly 0.45359237 kilograms, so conversions involving them can be as precise as you need.
Writing the units next to every number while you work is the simplest way to avoid mistakes. If the units do not cancel to leave the one you want, the calculation is set up wrongly.
For any value, use the PSI to Millimetres of mercury Converter or browse all pressure converters.
Run your own numbers: PSI to Millimetres of mercury Converter