Last updated: November 21, 2025

Barometric Pressure Conversion

Created by

Sarah K.

Reviewed by

CalcuTotal Team

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Convert weather station and aviation barometric pressures across common units.

Barometric Pressure Conversion formula

pressuretarget=pressuresource\text{pressure}_{\text{target}} = \text{pressure}_{\text{source}}

Barometric readings are normalized to Pascals, then expressed in meteorological units such as hPa, inHg, or mmHg; sea-level standard pressure is 1013.25 hPa (29.92 inHg).

Weather stations, aviation briefings, and lab logs switch between inches of mercury, hectopascals, millibars, and atmospheres. This converter keeps those readings consistent so you can compare altimeter settings, storm reports, or sensor calibrations without error.

How the conversion works

The tool normalizes every reading to Pascals (Pa), then rescales to the chosen unit. Anchors:

1 atm=101,325 Pa,1 inHg≈3,386.389 Pa,1 mmHg≈133.322 Pa1\,\text{atm} = 101{,}325\,\text{Pa}, \quad 1\,\text{inHg} \approx 3{,}386.389\,\text{Pa}, \quad 1\,\text{mmHg} \approx 133.322\,\text{Pa}

Standard sea-level pressure is 1013.25 hPa=29.92 inHg1013.25\,\text{hPa} = 29.92\,\text{inHg}, a helpful sense-check when comparing readings.

Units and conversions

UnitSymbolRelation to Pa
HectopascalhPa1 hPa=100 Pa1\,\text{hPa} = 100\,\text{Pa}
Millibarmbar1 mbar=100 Pa1\,\text{mbar} = 100\,\text{Pa}
KilopascalkPa1 kPa=1,000 Pa1\,\text{kPa} = 1{,}000\,\text{Pa}
PascalPabase unit
Inch of mercuryinHg1 inHg≈3,386.389 Pa1\,\text{inHg} \approx 3{,}386.389\,\text{Pa}
Millimetre of mercurymmHg1 mmHg≈133.322 Pa1\,\text{mmHg} \approx 133.322\,\text{Pa}
Atmosphereatm1 atm=101,325 Pa1\,\text{atm} = 101{,}325\,\text{Pa}
Barbar1 bar=100,000 Pa1\,\text{bar} = 100{,}000\,\text{Pa}

Worked examples

  1. Aviation altimeter setting in inHg → hPa
    Given 30.12 inHg30.12\,\text{inHg}:

    PhPa=30.12×3,386.389100≈1,021.0 hPaP_{\text{hPa}} = 30.12 \times \frac{3{,}386.389}{100} \approx 1{,}021.0\,\text{hPa}

    Result: 1,021.0 hPa.

  2. Weather station reading in hPa → inHg
    Given 1,018 hPa1{,}018\,\text{hPa}:

    PinHg=1,018×1003,386.389≈30.06 inHgP_{\text{inHg}} = 1{,}018 \times \frac{100}{3{,}386.389} \approx 30.06\,\text{inHg}

    Result: 30.06 inHg.

Tips and pitfalls

  • hPa and mbar are numerically identical; use whichever your audience expects.
  • Verify whether your sensor outputs station pressure or sea-level corrected pressure before comparing to forecasts.
  • For high-altitude sites, expect lower station pressure; do not “correct” it twice.
  • Keep at least two decimal places in inHg for aviation; small deltas affect altitude calculations.

References and further reading

FAQs