How to Convert Millimetres of mercury to Inches of mercury (mmHg to inHg)
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 inches of mercury by hand, with examples and a quick-reference table.
The conversion
To convert millimetres of mercury to inches of mercury, multiply the value by 0.0393699602. To go the other way, divide by the same number (or multiply by 25.4000765065). For a quick estimate, multiply by about 0.039.
Inches of mercury = millimetres of mercury × 0.0393699602
Worked examples
- 3 mmHg = 0.11811 inHg
- 12.5 mmHg = 0.492125 inHg
- 75 mmHg = 2.9527 inHg
Millimetres of mercury to Inches of mercury table
| Millimetres of mercury | Inches of mercury |
|---|---|
| 1 mmHg | 0.03937 inHg |
| 2 mmHg | 0.07874 inHg |
| 5 mmHg | 0.19685 inHg |
| 10 mmHg | 0.3937 inHg |
| 20 mmHg | 0.787399 inHg |
| 25 mmHg | 0.984249 inHg |
| 50 mmHg | 1.9685 inHg |
| 100 mmHg | 3.937 inHg |
| 250 mmHg | 9.8425 inHg |
| 500 mmHg | 19.685 inHg |
| 1,000 mmHg | 39.37 inHg |
Common questions
Is mmHg to inHg 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 Inches of mercury to Millimetres of mercury converter.
Mistakes to avoid
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
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.
Background
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.
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.
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.
For any value, use the Millimetres of mercury to Inches of mercury Converter or browse all pressure converters.
Run your own numbers: Millimetres of mercury to Inches of mercury Converter