Barometric Pressure Converter
Convert barometric pressure between hectopascals, millibars, inches of mercury and more.
Last updated · View algorithm, constants and default inputs (JSON)
Hectopascals (hPa)
About this calculator
Weather reports quote pressure in whatever unit the country uses, so the same system is 1013 hPa in Europe and 29.92 inHg in the United States. Converting between them matters when comparing forecasts or setting an altimeter.
Worked example
calculated with the default values below
Pressure value 1,013.25 · Unit Hectopascals (hPa) · Altitude (for sea-level correction) 0 ft Hectopascals 1,013.25 hPa · Millibars 1,013.25 mb · Inches of mercury 29.921 inHg · Millimetres of mercury 760.00 mmHg · Kilopascals 101.325 kPa · Atmospheres 1.00000 atm · Pounds per square inch 14.696 psi · Equivalent at sea level 1,013.25 hPa · Sea-level pressure category (rough) Near average
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
p = v × k ÷ 100; p₀ = p + 0.12 a
- v
- Input value
- k
- Factor to pascals
- p
- Pressure in hPa
- a
- Altitude, m
- p₀
- Sea-level pressure, hPa
k per unit: hPa/mb 100, kPa 1000, inHg 3386.389, atm 101325; the sea-level value adds 0.12 hPa per metre of altitude.
Frequently asked questions
What does the sea-level pressure category mean?
The category compares the estimated sea-level pressure with simple 1,000/1,020 hPa thresholds. Sea-level pressure uses station pressure plus altitude × 0.12 hPa, a linear approximation; it can drift at high elevation and does not account for temperature or humidity. Use a weather station or official forecast for interpretation.