mmHg to Inches of Mercury Converter
Common Conversions
| mmHg | inHg |
|---|---|
| 1 | 0.03937 |
| 5 | 0.19685 |
| 10 | 0.3937 |
| 25 | 0.9843 |
| 25.4 | 1 |
| 50 | 1.9685 |
| 100 | 3.937 |
| 250 | 9.843 |
| 500 | 19.685 |
| 760 | 29.921 |
| 1000 | 39.37 |
| 2000 | 78.74 |
Why this conversion matters in chemistry
Lab mercury manometers are graduated in mmHg by definition; older US vacuum-regulator dials are marked in inHg. A 760 mmHg atmospheric reading is 29.92 inHg on a legacy dial — the bridge value used in qualification runs before retiring an old dial gauge in favor of a digital pressure transducer. A factor of 1/25.4 inHg per mmHg reduces to the inch's exact definition (25.4 mm). It's the unit step at the boundary of SI-aligned mercury manometry and US legacy pressure equipment.
Formula
inHg = mmHg ÷ 25.4
Worked Examples
760 mmHg = 29.921 inHg
Standard atmospheric pressure expressed in both unit systems.
25.4 mmHg = 1 inHg
The exact conversion anchor — one inch of mercury in mm.
100 mmHg = 3.937 inHg
About a typical low-vacuum gauge reading.
500 mmHg = 19.685 inHg
About 2/3 of standard atmospheric pressure.
Frequently Asked Questions
How do I convert mmHg to inHg?
Divide by 25.4. So 760 mmHg becomes 29.92 inHg — standard atmospheric pressure. The factor is exact through the international inch definition.
Why does this conversion show up?
Communicating vacuum or pressure data to US-side industrial partners working in inHg, or cross-referencing barometric readings from a US weather station against lab pressure data in mmHg.
Is mmHg still commonly used?
Yes — mmHg (equivalently torr) remains the standard for vapor pressure, blood pressure, and many vacuum-system specifications. Modern chemistry largely uses kPa or bar, but mmHg survives in older equipment and clinical practice.