How to Convert Atmospheres to Inches of mercury (atm 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 atmospheres into inches of mercury by hand, with examples and a quick-reference table.
The conversion
To convert atmospheres to inches of mercury, multiply the value by 29.9212524019. To go the other way, divide by the same number (or multiply by 0.0334210609). For a quick estimate, multiply by about 30.
Inches of mercury = atmospheres × 29.9212524019
Worked examples
- 3 atm = 89.7638 inHg
- 12.5 atm = 374.0157 inHg
- 75 atm = 2,244.09 inHg
Atmospheres to Inches of mercury table
| Atmospheres | Inches of mercury |
|---|---|
| 1 atm | 29.9213 inHg |
| 2 atm | 59.8425 inHg |
| 5 atm | 149.6063 inHg |
| 10 atm | 299.2125 inHg |
| 20 atm | 598.425 inHg |
| 25 atm | 748.0313 inHg |
| 50 atm | 1,496.06 inHg |
| 100 atm | 2,992.13 inHg |
| 250 atm | 7,480.31 inHg |
| 500 atm | 14,960.63 inHg |
| 1,000 atm | 29,921.25 inHg |
Common questions
Is atm 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 Atmospheres 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.
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.
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
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.
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.
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 Atmospheres to Inches of mercury Converter or browse all pressure converters.
Run your own numbers: Atmospheres to Inches of mercury Converter