Millimetres of mercury (conventional) to pounds per square inch (mmHg to psi)

The formula

psi = mmHg × 0.01933677746

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

• 1 mmHg = 13.5951 × g / cm³ × gₙ (standard gravity, CODATA 2022) × m / s² × mm = 133.322387415 Pa
• 1 psi = lbf / in² = 6,894.75729317 Pa

Dividing the two SI sizes gives the factor: 0.0193367774595 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 51.7149252039.

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): 1,654.88 mmHg = 32 psi — 1,654.88 × 0.01933677746 = 32
• Sea-level air (1 atm): 760 mmHg = 14.6959 psi — 760 × 0.01933677746 = 14.6959
• A car tyre (European gauge) (2.2 bar): 1,650.14 mmHg = 31.9083 psi — 1,650.14 × 0.01933677746 = 31.9083
• A systolic blood-pressure reading: 120 mmHg = 2.32041 psi — 120 × 0.01933677746 = 2.32041

Frequently asked questions