Convert Millimeters of Water to Feet of Water
Convert Millimeters of Water (mmH₂O) to Feet of Water (ftH₂O) instantly and accurately.
Conversion Formula
ftH₂O = mmH₂O × 0.003280839895
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 Feet of Water
One foot of water column (ftH₂O) ≈ 2,989 Pa - the US customary equivalent of cmH₂O used in civil and hydraulic engineering. Municipal water supply systems are designed for 40-80 psi head ≈ 92-184 ft; fire suppression sprinkler systems require minimum 7 psi ≈ 16 ft. Well pump specifications, sump pump head ratings, irrigation mainline pressure, and drainage calculations all use feet of head. 1 ft of water = 12 in WC = 0.4335 psi ≈ 2,989 Pa.
Quick Reference Table
| Millimeters of Water (mmH₂O) | Feet of Water (ftH₂O) |
|---|---|
| 1 mmH₂O | 0.00328084 ftH₂O |
| 2 mmH₂O | 0.00656168 ftH₂O |
| 5 mmH₂O | 0.0164042 ftH₂O |
| 10 mmH₂O | 0.0328084 ftH₂O |
| 25 mmH₂O | 0.082021 ftH₂O |
| 50 mmH₂O | 0.164042 ftH₂O |
| 100 mmH₂O | 0.328084 ftH₂O |