Inches of mercury (conventional) to hectopascals (inHg to hPa)

The formula

hPa = inHg × 33.8638864

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

• 1 inHg = 13.5951 × g / cm³ × gₙ (standard gravity, CODATA 2022) × m / s² × in = 3,386.38864034 Pa
• 1 hPa = 100 × Pa = 100 Pa

Dividing the two SI sizes gives the factor: 33.8638864034 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.029529983301.

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): 65.1527 inHg = 2,206.32 hPa — 65.1527 × 33.8638864 = 2,206.32
• Sea-level air (1 atm): 29.9213 inHg = 1,013.25 hPa — 29.9213 × 33.8638864 = 1,013.25
• A car tyre (European gauge) (2.2 bar): 64.966 inHg = 2,200 hPa — 64.966 × 33.8638864 = 2,200
• A systolic blood-pressure reading (120 mmHg): 4.72441 inHg = 159.987 hPa — 4.72441 × 33.8638864 = 159.987

Frequently asked questions