Convert Millimeters of Water to Pounds per Square Inch
Convert Millimeters of Water (mmH₂O) to Pounds per Square Inch (psi) instantly and accurately.
Conversion Formula
psi = mmH₂O × 0.001422334331
About Millimeters of Water
One millimetre of water column (mmH₂O) = pressure from 1 mm of fresh water at standard gravity = exactly 9.80665 Pa. Preferred for very low differential pressures in HVAC: ductwork static pressures, fan curves, filter resistance, and building pressurisation are in mm WC. Gas valve operating pressures are typically 0.5-3 mm WC; clean-room cascade differentials 12-25 mm WC. A domestic gas hob manifold operates at ~20 mm WC on natural gas. Also used in spirometer calibration and hospital oxygen delivery systems. 1 mmH₂O = 9.80665 Pa.
About Pounds per Square Inch
One pound per square inch (psi) ≈ 6,894.76 Pa - the dominant pressure unit in US industry and consumer products. Car tyres: 32-36 psi; truck tyres 80-120 psi; bicycle road tyres 80-130 psi. Home water supply: 40-80 psi; residential maximum 80 psi per plumbing code. Compressed air tools: 90-150 psi. Steam autoclave sterilisation: 15-30 psi. The distinction between gauge (psig) and absolute (psia) pressure is critical: gauge pressure is relative to ambient; absolute = gauge + ~14.696 psi. 1 psi = 6,894.76 Pa.
Quick Reference Table
| Millimeters of Water (mmH₂O) | Pounds per Square Inch (psi) |
|---|---|
| 1 mmH₂O | 0.00142233 psi |
| 2 mmH₂O | 0.00284467 psi |
| 5 mmH₂O | 0.00711167 psi |
| 10 mmH₂O | 0.0142233 psi |
| 25 mmH₂O | 0.0355584 psi |
| 50 mmH₂O | 0.0711167 psi |
| 100 mmH₂O | 0.142233 psi |