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Pressure vs Barometric Pressure Conversion

Compare six pressure units with a nine-unit converter that adds hPa, mbar and inHg, including their actual factors and rounding.

Pressure Converter Calculator

Convert Pa, kPa, bar, atm, psi, and mmHg in one pressure hub with formulas, reference factors, and gauge-versus-absolute guidance.

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Barometric Pressure Conversion

Convert barometric pressure readings among hPa, millibars, inHg, mmHg, kPa, Pa, bar, atm, and psi for weather, aviation, and lab records.

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At a glance

DetailPressure Converter CalculatorBarometric Pressure Conversion
CategoryConversionConversion
What it doesConvert Pa, kPa, bar, atm, psi, and mmHg in one pressure hub with formulas, reference factors, and gauge-versus-absolute guidance.Convert barometric pressure readings among hPa, millibars, inHg, mmHg, kPa, Pa, bar, atm, and psi for weather, aviation, and lab records.

The pressure converter offers Pa, kPa, bar, atm, psi and mmHg. Barometric pressure conversion adds hPa, mbar and inHg. Both have a value plus source/target selectors and convert through pascals.

Pressure converterBarometric pressure conversion
InputNonnegative value; default 101325 Pa to atmNonnegative pressure; default 1013.25 hPa to inHg
Psi factor4.4482216152605 ÷ 0.0254² PaSame dimensional psi factor
mmHg factor133.3224 Pa133.322387415 Pa
inHg factorNot supported3386.388640341 Pa
Primary displayPa: 2 fixed decimals; others: 6 fixed decimalsUp to 4 decimal places
DetailsAll six unitsPa, atm, bar and selected conversion factor

Both use 1 atm = 101325 Pa. In the larger menu, hPa and mbar each equal 100 Pa, so they convert one-to-one.

Compare the same input

For 35 psi to kPa, the hub evaluates 35 × (4.4482216152605 ÷ 0.0254²) ÷ 1000. The unrounded value is approximately 241.316505260893 kPa, displayed 241.316505 kPa. Its psi factor is derived from the exact inch and pound-force definitions, rather than the old rounded 6894.76 Pa factor.

The barometric default returns 29.9213 inHg from 1013.25 hPa. Its longer mmHg constant differs slightly from the hub’s stated 133.3224 Pa approximation; neither difference establishes instrument accuracy.

Reference and scope

Choose the form with the units required by your source and destination. Preserve whether the stated value is gauge or absolute: a proportional unit change does not add or subtract atmospheric pressure. Neither form performs gauge-to-absolute conversion, altitude correction or sea-level reduction. Unit conversion alone does not select an equipment setting or interpret a measurement.

Sources

NIST SP 811, unit definitions and Appendix B factors. The paired calculator controls and rounding described above are their current form behavior.

Frequently asked questions

Do these forms use different psi factors?
No. Both derive psi from 4.4482216152605 N per pound-force and the exact inch area. Their mmHg constants and display precision differ.
Are hPa and mbar equal?
Yes. Both equal 100 Pa and are included in the barometric menu.
Does either form correct pressure for altitude?
No. These are unit conversions and preserve the stated pressure reference.

Sources

  • Source document (www.nist.gov)

    primary · Aug 14, 2026

    Supports: Table 9 bar = 100000 Pa and standard atmosphere = 101325 Pa; Appendix B exact pound-force and inch factors; mmHg factors are stated current-model constants

    — vNIST SP 811, 2008 edition

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