mmHg to atm Converter

One standard atmosphere is 760 mmHg, the height of mercury it supports in a barometer. Medical and laboratory readings in mmHg convert this way.

How to use the mmHg to atm Converter

1. Type the number of millimetres of mercury into the Millimetres of mercury field. Decimals such as 380 are fine.
2. Read the answer in Standard atmospheres – it updates as you type, with no button to press.
3. To convert the other way, type into Standard atmospheres and the millimetres of mercury are recalculated.
4. Press Copy results to copy both values with the page title, or Copy link to share this exact conversion.

This page converts only mmHg ⇄ atm. Need a different unit? Use the general pressure converter, where you can choose any “from” and “to” unit.

How it works

Both units measure pressure, so they are always in the same ratio: one millimetre of mercury equals 0.0013157897 standard atmospheres. The calculator multiplies the number of millimetres of mercury you type by 0.0013157897 to give standard atmospheres, and when you type into the standard atmospheres field it divides by the same factor to give millimetres of mercury. Because the ratio never changes, doubling the millimetres of mercury always doubles the standard atmospheres. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation).

How to convert millimetres of mercury to standard atmospheres

1. Write down the value in millimetres of mercury, for example 760 mmHg.
2. Multiply by the conversion factor 0.0013157897 (because 1 millimetre of mercury = 0.0013157897 atm).
3. 760 × 0.0013157897 = 1.0000001 atm.
4. To go back from standard atmospheres to millimetres of mercury, divide by 0.0013157897 – or multiply by 759.99989.

mmHg to atm conversion table

What is a millimetre of mercury?

Millimetres of mercury measure pressure by the height of a mercury column. Blood pressure is reported in mmHg, and 760 mmHg is one standard atmosphere.

What is a standard atmosphere?

The standard atmosphere is exactly 101,325 Pa, the average air pressure at sea level. Chemistry problems and diving depth calculations often use atm.

Quick mental conversion

For a fast estimate, multiply millimetres of mercury by about 0.0013 to get standard atmospheres; the error is about 1.2%. Use the calculator above when you need the exact figure.

Common mistakes to avoid

Mixing gauge pressure (psig, barg) with absolute pressure (psia, bara), treating bar and atm as identical, and confusing kgf/cm² with bar.