Convert Atmospheres to Millimeters of Mercury

Formula

mmHg = atm × 759.9998917256

Derivation from SI units:

• 1 atm = 101 325 Pa (exact, by definition)
• 1 mmHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.001 m = 133.322387415 Pa
• 1 atm = 101325 Pa ÷ 133.322387415 Pa per mmHg = 759.9998917256 mmHg

Both units are defined exactly, so the factor is exact. Atmosphere definition: atmosphere; Millimeter of Mercury definition: millimeter of mercury.

Worked examples

1. A reading of 1.5 atm converts to 1139.999838 mmHg.
   1.5 atm × 759.9998917 = 1139.999838 mmHg
2. A value of 10 atm is 7599.998917 mmHg.
   10 atm × 759.9998917 = 7599.998917 mmHg

Where it's used

Atmospheres are used for chemistry and gas laws (STP and NTP conditions), while millimeters of mercury appear in blood pressure (e.g. 120/80 mmHg). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.

Atmosphere to other pressure units

Frequently asked questions

Sources

• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "atmosphere, standard (atm)".
• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "millimeter of mercury, conventional (mmHg)".

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.