Convert pressure values between psi, kPa, Pa, MPa, bar, atm, Torr, mmHg, inHg, and water-column units with quick checks that help prevent unit mix-ups.
Advanced options
How to use our Pressure Conversion Calculator
- Enter the number in Pressure value, then choose its unit in Convert from.
- Choose your target unit in Convert to and pick how many digits to show in Rounded to.
- Click Calculate to see Converted pressure, a short Common equivalent values list, and How the conversion was done.
- Sanity-check the answer by looking at Common equivalent values: for example, about 1 atm should be about 14.7 psi, 101.325 kPa, and 1.01325 bar.
- Read Unit note when you use Torr, mmHg, inHg, or water-column units, because reference conditions and definitions can slightly change the result.
Definitions
Pressure value: The number you want to convert before any unit change.
Pa (pascal): The SI base pressure unit used as the calculator's middle step.
kPa: Kilopascal, equal to 1,000 Pa.
MPa: Megapascal, equal to 1,000,000 Pa.
bar: A common engineering pressure unit equal to 100,000 Pa.
atm: Standard atmosphere, equal to 101,325 Pa.
Torr: A pressure unit defined as exactly 1/760 of a standard atmosphere.
mmHg (0 deg C): Millimeters of mercury at 0 deg C. It is extremely close to Torr, but not exactly identical by definition [2].
inHg (0 deg C): Inches of mercury at 0 deg C. The 0 deg C part matters because the column definition depends on reference conditions.
inH2O (4 deg C) and ftH2O (4 deg C): Water-column pressure units based on water at 4 deg C, so the reference temperature must stay attached to the unit [2].
Significant figures: The number of meaningful digits shown in the displayed answer after rounding.
Common mistakes and quick fixes
Mistake: Leaving Pressure value blank or typing text that is not a number.
Fix: Enter a numeric value in Pressure value , such as 14.7 or 101.325.
Mistake: Picking the wrong starting unit in Convert from , such as entering psi but leaving kPa selected.
Fix: Match Convert from to the unit of the number you actually typed before reading Converted pressure .
Mistake: Treating Torr and mmHg (0 deg C) as exactly the same in every case.
Fix: Check Unit note and use the exact unit your source gives, especially when accuracy matters.
Mistake: Ignoring the reference condition in inHg (0 deg C) , inH2O (4 deg C) , or ftH2O (4 deg C) .
Fix: Keep the full unit name in mind and read Unit note so you do not swap mercury-column and water-column values.
Mistake: Using too few digits in Rounded to and thinking two close units are identical.
Fix: Increase Rounded to to 6 or 8 significant figures when comparing Torr , mmHg (0 deg C) , or other very close values.
Mistake: Assuming a negative Converted pressure must be wrong.
Fix: Negative results can be valid for differential or gauge-style readings if your original Pressure value was negative.
Limitations & Key Assumptions / Boundary Conditions
- This calculator converts units only. It does not decide whether a reading is gauge pressure, absolute pressure, or differential pressure for you.
- Torr and mmHg are very close, but they are not exactly the same by definition, so tiny differences can appear.
- Water-column and mercury-column units depend on stated reference conditions, so results apply only to the exact forms shown in the unit labels.
- Displayed answers are rounded, but internal math stays unrounded until the final display step.
- Very large or very small results may be shown in scientific notation when a normal decimal would be hard to read.
- If your source uses a different reference temperature or a different unit definition, your real-world value can differ slightly from this result.
Methodology
Conversion method
The calculator uses one base unit so every conversion stays consistent. It first changes your input into pascals, then changes pascals into the target unit.
value_Pa = input_value * Pa_per_from_unit
output_value = value_Pa / Pa_per_to_unit
Unit factors used
1 atm = 101325 Pa
1 bar = 100000 Pa
1 mbar = 100 Pa
1 kPa = 1000 Pa
1 MPa = 1000000 Pa
1 psi = 6894.757293168 Pa
1 Torr = 101325 / 760 Pa
1 mmHg = 133.322387415 Pa
1 inHg = 3386.38815789 Pa
1 inH2O = 249.08891 Pa
1 ftH2O = 2989.06692 Pa
Worked example
If you enter 14.7 in Pressure value, choose psi in Convert from, and choose kPa in Convert to, the calculator does two steps.
value_Pa = 14.7 * 6894.757293168 = 101352.93220957 Pa
output_value = 101352.93220957 / 1000 = 101.35293220957 kPa
With 6 significant figures, the displayed Converted pressure is 101.353 kPa.
How notes are triggered
If either selected unit is Torr, mmHg, inHg, inH2O, or ftH2O, the calculator shows a short Unit note. This helps flag cases where definitions are close but not identical, or where reference temperature is part of the unit name [1][2].
Assumptions used in results
The calculator assumes the exact conversion factors listed above, keeps negative signs if you entered a negative pressure, and rounds only for display. That means small display differences can appear when you choose fewer significant figures or compare nearly equal units such as Torr and mmHg.