This converter turns inches of mercury into millimeters of mercury instantly, using the exact factor 1 inch of mercury = 25.4000027 millimeters of mercury. Type any number and the result updates as you go — nothing is sent to a server, so the arithmetic happens entirely in your browser.
US aviation and weather altimeter setting unit. The clinical unit for blood pressure worldwide.
Because the relationship is a simple proportion, one multiplication does the whole job. The table further down gives pre-computed values for the amounts people look up most often, and the result panel also reports the reverse conversion so you can check the figure both ways.
The formula
inches of mercury- The amount you are converting, measured in inches of mercury
25.4000027- The exact number of millimeters of mercury in one inch of mercury
millimeters of mercury- The converted result
How it works, step by step
- Enter the number of inches of mercury you want to convert.
- The value is multiplied by 25.4000027, the exact conversion factor.
- The result is displayed in millimeters of mercury, rounded for readability.
- The unrounded value and the reverse conversion appear underneath so you can verify it.
Worked examples
Converting 5 inches of mercury
Multiply 5 by 25.400003. That gives 127 millimeters of mercury. A quick sanity check: one inch of mercury is larger than one millimeter of mercury, so the number should get bigger — and it does.
Converting 72 inches of mercury
72 × 25.400003 = 1,828.8 millimeters of mercury. Working backwards, 1,828.8 ÷ 25.400003 returns 72 inches of mercury, which confirms the factor is applied the right way round.
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Frequently asked questions
How many millimeters of mercury are in one inch of mercury?
Exactly 25.4000027. Every conversion on this page is that single number multiplied by your input, so the result carries no rounding error beyond what is shown.
What is the formula to convert inches of mercury to millimeters of mercury?
Millimeters Of Mercury = inches of mercury × 25.4000027. To reverse it, divide instead: inches of mercury = millimeters of mercury ÷ 25.4000027, which is the same as multiplying by 0.03937007456.
Is the inch of mercury bigger than the millimeter of mercury?
Yes. One inch of mercury equals 25.4 millimeters of mercury, so it is the larger unit.
Why does my answer differ slightly from other inhg to mmhg converters?
Most differences come from rounding the factor too early. This tool keeps full double precision through the calculation and only rounds at the final display step, and it also shows the unrounded value so you can see exactly where any difference appears.
What is a inch of mercury?
US aviation and weather altimeter setting unit.
What is a millimeter of mercury?
The clinical unit for blood pressure worldwide.
Inches Of Mercury to millimeters of mercury reference table
| Inches Of Mercury | Millimeters Of Mercury |
|---|---|
| 0.5 inHg | 12.7 mmHg |
| 1 inHg | 25.4 mmHg |
| 2 inHg | 50.8 mmHg |
| 3 inHg | 76.2 mmHg |
| 5 inHg | 127 mmHg |
| 10 inHg | 254 mmHg |
| 15 inHg | 381 mmHg |
| 20 inHg | 508.0001 mmHg |
| 25 inHg | 635.0001 mmHg |
| 50 inHg | 1,270 mmHg |
| 75 inHg | 1,905 mmHg |
| 100 inHg | 2,540 mmHg |
| 250 inHg | 6,350 mmHg |
| 500 inHg | 12,700 mmHg |
| 1000 inHg | 25,400 mmHg |
Exact factor: 1 inch of mercury = 25.4000027 millimeters of mercury. Values rounded for display.