How to Convert Inches of mercury to Millimetres of mercury (inHg 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 inches of mercury into millimetres of mercury by hand, with examples and a quick-reference table.
The conversion
To convert inches of mercury to millimetres of mercury, multiply the value by 25.4000765065. To go the other way, divide by the same number (or multiply by 0.0393699602). For a quick estimate, multiply by about 25.
Millimetres of mercury = inches of mercury × 25.4000765065
Worked examples
- 3 inHg = 76.2002 mmHg
- 12.5 inHg = 317.501 mmHg
- 75 inHg = 1,905.01 mmHg
Inches of mercury to Millimetres of mercury table
| Inches of mercury | Millimetres of mercury |
|---|---|
| 1 inHg | 25.4001 mmHg |
| 2 inHg | 50.8002 mmHg |
| 5 inHg | 127.0004 mmHg |
| 10 inHg | 254.0008 mmHg |
| 20 inHg | 508.0015 mmHg |
| 25 inHg | 635.0019 mmHg |
| 50 inHg | 1,270 mmHg |
| 100 inHg | 2,540.01 mmHg |
| 250 inHg | 6,350.02 mmHg |
| 500 inHg | 12,700.04 mmHg |
| 1,000 inHg | 25,400.08 mmHg |
Common questions
Is inHg 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 Inches of mercury converter.
Mistakes to avoid
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.
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.
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 Inches of mercury to Millimetres of mercury Converter or browse all pressure converters.
Run your own numbers: Inches of mercury to Millimetres of mercury Converter