Inches of Mercury to mmHg Converter
Common Conversions
| inHg | mmHg |
|---|---|
| 0.1 | 2.54 |
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 29.921 | 760 |
| 50 | 1270 |
| 100 | 2540 |
Why this conversion matters in chemistry
The conversion is exact: both units measure the same physical mercury column, just in different length units. Since 1 inch is defined as exactly 25.4 mm, 29.921 inHg of standard atmospheric pressure becomes 760 mmHg without any rounding. The factor comes up most when a US barometer reading has to land on a vapor-pressure table written in mmHg, or when a boiling-point correction needs the local barometric pressure expressed in chemistry units. Both ends of the conversion describe the same physics — a column of mercury at standard gravity — so there's no fudge in the factor.
Formula
Worked Examples
Standard atmospheric pressure — the calibration reference in both unit conventions.
The defining identity — exactly 25.4 mm to an inch, locked by the 1959 international yard and pound agreement.
A reduced barometric reading you might see on a high-altitude weather report or in a partially evacuated apparatus.
A low-pressure measurement, the kind shown on a vacuum gauge during a moderate-vacuum operation.