How to Convert Inches of mercury to PSI (inHg to psi)
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 psi by hand, with examples and a quick-reference table.
The conversion
To convert inches of mercury to psi, multiply the value by 0.4911542205. To go the other way, divide by the same number (or multiply by 2.0360203745). For a quick estimate, multiply by about 0.49.
PSI = inches of mercury × 0.4911542205
Worked examples
- 3 inHg = 1.4735 psi
- 12.5 inHg = 6.1394 psi
- 75 inHg = 36.8366 psi
Inches of mercury to PSI table
| Inches of mercury | PSI |
|---|---|
| 1 inHg | 0.491154 psi |
| 2 inHg | 0.982308 psi |
| 5 inHg | 2.4558 psi |
| 10 inHg | 4.9115 psi |
| 20 inHg | 9.8231 psi |
| 25 inHg | 12.2789 psi |
| 50 inHg | 24.5577 psi |
| 100 inHg | 49.1154 psi |
| 250 inHg | 122.7886 psi |
| 500 inHg | 245.5771 psi |
| 1,000 inHg | 491.1542 psi |
Common questions
Is inHg to psi 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 PSI to Inches of mercury 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.
Mixing similar-sounding units
US and imperial gallons, pints and tons are different sizes, and decimal kilobytes differ from binary kibibytes.
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
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 Inches of mercury to PSI Converter or browse all pressure converters.
Run your own numbers: Inches of mercury to PSI Converter