Barometric Pressure Converter

Conversion

Convert a barometric (atmospheric) pressure reading between the units used in weather and aviation: hectopascals/millibars (hPa/mb), inches of mercury (inHg), millimetres of mercury (mmHg), kilopascals (kPa), and standard atmospheres (atm). Enter your reading and its unit to see all the equivalents.

Formula

Convert the reading to pascals, then to every other unit (1 hPa = 100 Pa, 1 inHg = 3386.389 Pa, 1 mmHg = 133.322 Pa, 1 atm = 101,325 Pa)
  • Standard sea-level pressure is 1013.25 hPa = 29.92 inHg = 760 mmHg = 1 atm.
  • Weather reports often use hPa/mb (the same value) or inHg in the US.
  • Aviation altimeter settings ('QNH') are given in hPa or inHg depending on the region.
  • Mercury-based units (inHg, mmHg) come from the height of a mercury column the pressure can support.

Convert 1013.25 hPa

Inputs
  • Pressure Reading: 1013.25
  • Input Unit: hpa

1013.25 hPa is standard sea-level pressure. It equals 29.92 inHg, 760 mmHg, 101.325 kPa, and exactly 1 atm.

Frequently asked questions

What is standard barometric pressure?
At sea level it's defined as 1013.25 hPa (millibars), which is the same as 29.92 inHg, 760 mmHg, or 1 standard atmosphere.
Are hPa and mb the same?
Yes — one hectopascal equals exactly one millibar, so weather services use the numbers interchangeably.
Why is pressure measured in inches of mercury?
Early barometers used a column of mercury; the pressure was read as the height the mercury rose, so inHg and mmHg are still used today, especially in weather and aviation.
How do I convert hPa to inHg?
Divide the hPa value by 33.8639. For example, 1013.25 hPa ÷ 33.8639 ≈ 29.92 inHg.