Hectopascals to millimetres of mercury (conventional) (hPa to mmHg)

The formula

mmHg = hPa × 0.7500615758

Where the factor comes from — each unit by its definition, then its size in SI:

• 1 hPa = 100 × Pa = 100 Pa
• 1 mmHg = 13.5951 × g / cm³ × gₙ (standard gravity, CODATA 2022) × m / s² × mm = 133.322387415 Pa

Dividing the two SI sizes gives the factor: 0.750061575846 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 1.33322387415.

Pressure is force per area; the pascal is one newton per square metre. Tyres are quoted in psi or bar, weather in hPa, blood pressure in mmHg and gas laws in pascals or atmospheres.

Worked examples

• A car tyre (US gauge) (32 psi): 2,206.32 hPa = 1,654.88 mmHg — 2,206.32 × 0.7500615758 = 1,654.88
• Sea-level air (1 atm): 1,013.25 hPa = 760 mmHg — 1,013.25 × 0.7500615758 = 760
• A car tyre (European gauge) (2.2 bar): 2,200 hPa = 1,650.14 mmHg — 2,200 × 0.7500615758 = 1,650.14
• A systolic blood-pressure reading: 159.987 hPa = 120 mmHg — 159.987 × 0.7500615758 = 120

Frequently asked questions