Pressure
Convert pound per square inch (psi) to inch of water column (inH₂O). Pressure is force per unit area. Process engineers move constantly between SI (kPa, bar) and US (psi) units, and between absolute and gauge.
1 psi = 27.6799 inH₂O
To convert pound per square inch to inch of water column, multiply the psi value by 27.6799. To go the other way, divide by 27.6799 (or multiply by 0.03612729).
| psi | inH₂O |
|---|---|
| 1 | 27.6799 |
| 2 | 55.35981 |
| 5 | 138.3995 |
| 10 | 276.799 |
| 25 | 691.9976 |
| 50 | 1383.995 |
| 100 | 2767.99 |
| 250 | 6919.976 |
| 500 | 13839.95 |
| 1000 | 27679.9 |
Line and vessel ratings, pump discharge heads, and relief set points are all specified in pressure units — usually psi or barg in the field and kPa in calculations.
Always track whether a value is absolute or gauge: 0 barg equals about 101.3 kPa absolute, and mixing the two is a common and costly error.
Worked example. A pressure of 145.0377 psi is 4014.631 inH₂O.
Multiply the value in psi by 27.6799 to get inH₂O. For example, 10 psi = 276.799 inH₂O.
1 psi equals 27.6799 inH₂O.
Line and vessel ratings, pump discharge heads, and relief set points are all specified in pressure units — usually psi or barg in the field and kPa in calculations.