ParrotNotes

Pressure Conversion Calculator

Convert pressure between psi, bar, kPa, MPa, inches of water, inches of mercury, feet of head and atmospheres, with gauge and absolute pressure. Type one value, pick its unit and see it in all 16 units at once, plus a table of common psi and bar values.

Your numbers

The figure from the gauge, the data sheet or the call. A pressure difference converts the same way.

Gauge reads zero at atmospheric pressure; absolute reads zero at a full vacuum. Pick one to see the other reading too.

In bar

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Pascals (Pa)
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Kilopascals (kPa)
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Megapascals (MPa)
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Millibar (mbar, hPa)
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Kilopounds per square inch (ksi)
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Standard atmospheres (atm)
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Technical atmospheres, kgf/cm² (at)
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Torr
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Millimeters of mercury (mmHg)
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Inches of mercury (inHg)
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Inches of water (inHâ‚‚O, in. w.c.)
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Feet of water, feet of head (ftHâ‚‚O)
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Millimeters of water (mmHâ‚‚O)
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Meters of water (mHâ‚‚O)
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Factors from NIST SP 811, Appendix B.9. Water-column units (inH₂O, ftH₂O, mmH₂O, mH₂O) use NIST's conventional values, 9.806 65 Pa per mm, a 1,000 kg/m³ column, about water at 4 °C (39.2 °F); a 60 °F inch of water is 0.1% smaller. Mercury columns use NIST's conventional values.

Gauge and absolute differ by the atmospheric pressure, not by a unit factor: convert the units first, then add or subtract it.

The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.

How pressure conversion works

Every pressure unit is a fixed number of pascals, so the calculator turns your value into Pa and then divides by the pascals in each other unit. All the rows come from that one number, so they agree with each other.

The factors are from NIST SP 811, the US National Institute of Standards and Technology guide to SI units, Appendix B.9. Some are exact by definition: 1 bar = 100,000 Pa, 1 atm = 101,325 Pa, 1 at (one kilogram-force per square centimeter) = 98,066.5 Pa. psi comes from the exact pound-force and inch: 1 psi = 6,894.757 Pa. Torr is 1/760 of a standard atmosphere.

Common pressure conversions

Quick values, worked out with the same factors as the calculator.

psi to bar and kPa
psibarkPa
10.06896.89
50.344734.47
100.689568.95
14.71.0135101.35
201.379137.9
302.0684206.84
402.7579275.79
503.4474344.74
604.1369413.69
805.5158551.58
1006.8948689.48
15010.34211,034.21
20013.78951,378.95
30020.68432,068.43
50034.47383,447.38
1,00068.94766,894.76
3,000206.842720,684.27
bar to psi and kPa
barpsikPa
0.57.2550
114.5100
1.521.76150
229.01200
343.51300
458.02400
572.52500
687.02600
8116.03800
10145.041,000
16232.061,600
25362.592,500
40580.154,000
1001,450.3810,000
2002,900.7520,000
2503,625.9425,000
3505,076.3235,000
Inches of water to Pa, mbar and psi
inHâ‚‚OPambarpsi
0.124.90.2490.0036
0.2562.30.6230.009
0.5124.51.2450.0181
1249.12.4910.0361
2498.24.9820.0723
3747.37.4730.1084
51,245.412.4540.1806
102,490.924.9090.3613
27.686,894.868.9481

Gauge and absolute pressure

A tire gauge, a hydraulic gauge and most process gauges read gauge pressure: zero is the air around them. Vacuum gauges, barometers, refrigerant tables and many transmitters read absolute pressure: zero is a full vacuum. The two differ by the atmospheric pressure, which is a quantity you add or subtract, not a unit factor.

Pick gauge or absolute and the page shows the other reading as well. It starts from the standard atmosphere, 101.325 kPa (14.696 psi); for a site at altitude or a precise reading, type the local barometric pressure.

Inches of water, feet of head and mercury

Water-column units measure the height of water a pressure holds up. They depend on the water's density, so NIST lists several. This page uses the conventional values, 9.806 65 Pa per millimeter, a column of 1,000 kg/m³ under standard gravity, which is about the density of water at 4 °C (39.2 °F): 1 inH₂O = 249.0889 Pa and 1 ftH₂O = 2,989.067 Pa. NIST's 60 °F inch of water is 248.84 Pa, about 0.1% less, so tables based on it differ in the fourth figure.

The flow rate calculator, linked below, works out flow, pipe velocity and the head a pump has to deliver, and it uses the 60 °F foot of water; this page only converts units. Mercury columns (mmHg, inHg) use NIST's conventional values; 1 mmHg and 1 Torr differ by less than one part in a million.

For HVAC, pump and hydraulics sales engineers and techs

Pressures come up on the site call and the supplier call in whatever unit the person has in front of them: a European pump curve in bar and meters of head, a US gauge in psi, a burner spec in inches of water, a vacuum pump in mbar or Torr. Note the unit and whether it is gauge or absolute every time; a missing g or a on a figure is a common source of a wrong quote.

Sources, each read on 2026-10-31. Round the result to the precision of the gauge or the spec you are working to:

Related: the flow rate calculator for flow, pipe velocity and pump head (it calculates; this page only converts units), and the torque conversion calculator for N·m, ft-lb and in-lb.

More for HVAC and industrial sales: HVAC sales, Industrial distributor, Sales engineer.

Specs get read out in mixed units

On a site call or a supplier call the pump curve comes in bar, the gauge in psi and the burner spec in inches of water, often in the same five minutes. Record the call in ParrotNotes and you get a transcript and a summary, so every figure and its unit is there in writing when you convert and quote.

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Pressure conversion FAQ