Convert air pressure to equivalent water-column pressure or head, reverse the conversion, and add compressed-air pressure to hydrostatic tank head.

Pressure is the same physical quantity in air and water. Convert gauge pressure to equivalent column height.

Optional settings

Blank = 998.2 kg/m³, approximately fresh water at 20°C. This affects actual column heights, not conventional pressure-unit definitions.

Air Pressure to Water Pressure Formula

At a static air-water boundary, the transmitted pressure has the same value in the same units and relative to the same reference. Equivalent water-column height also depends on water density and gravity.

Pw = Pₐ, h = (Pₐ) / (ρ g)

Variables:

  • Pw is the water pressure in psi
  • Pa is the air pressure in psi
  • For column height h in meters, use pressure in Pa, water density ρ in kg/m³ and gravity g = 9.80665 m/s²

The same gauge pressure in air and water has a one-to-one relationship. For water-column height, use h = P/(ρg). In a static air-over-water tank, add ρgh to the air-space gauge pressure to find outlet gauge pressure.

Air Pressure (psi) to Water Pressure (psi) Conversion Table (Same Pressure Reference)
Air Pressure (psi) Water Pressure (psi)
11
22
55
1010
1515
2020
2525
3030
3535
4040
5050
6060
8080
9090
100100
120120
140140
150150
175175
200200
Same static boundary and pressure reference: water pressure (psi) = air pressure (psi). About 0.433 psi per foot applies to water depth, not air PSI.

What is Air Pressure to Water Pressure Conversion?

Air and water can transmit the same pressure; changing the medium does not change PSI. A water-column height is different: pressure equals density times gravity times vertical height. At density 1000 kg/m³ and standard gravity, one foot produces about 0.43353 psi. Actual column height changes with density; conventional inH₂O is a defined pressure unit.

How to Calculate Air Pressure to Water Pressure?

The following steps outline how to calculate the water pressure from air pressure.

  1. First, determine the air pressure (Pa).
  2. Next, keep the same pressure reference. For column height, choose the water density and units.
  3. The pressure at the boundary is Pw = Pa. If calculating water head, divide pressure in pascals by ρg.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Air Pressure (Pa) = 100 psi

The water-side boundary pressure is also 100 psi. At density 1000 kg/m³, the equivalent water head is approximately 70.30696 m.