mmHg to Atmospheres Converter
Common Conversions
| mmHg | atm |
|---|---|
| 1 | 0.001316 |
| 10 | 0.01316 |
| 50 | 0.06579 |
| 100 | 0.1316 |
| 200 | 0.2632 |
| 380 | 0.5 |
| 500 | 0.6579 |
| 760 | 1 |
| 1000 | 1.3158 |
| 1520 | 2 |
| 2280 | 3 |
| 3800 | 5 |
Why this conversion matters in chemistry
The Dumas method for measuring a volatile liquid's molar mass is a classic example of why this conversion matters. You record the barometer reading in mmHg along with the flask volume and temperature, then use PV = nRT to back out moles. But R = 0.08206 L·atm/(mol·K) expects atm, not mmHg, so a barometric pressure of 748 mmHg has to get divided by 760 to become 0.9842 atm before it drops into the equation. Forgetting the division gives you an answer off by a factor of 760 — the kind of error that survives all the way through the calculation because the rest of the arithmetic looks fine.
Formula
Worked Examples
The defining equivalence. 760 mmHg was the original definition of the standard atmosphere before the pascal took over.
Half an atmosphere. Typical working vacuum for distillation of a moderately volatile solvent.
Water's vapor pressure at 25°C. The correction you apply when collecting a gas over water and needing the actual partial pressure of the dry gas.
Roughly the absolute pressure inside a steam autoclave at 121°C — enough to push water's boiling point above the sterilization threshold.