Convert Feet of Water to Millimeters of Water
Convert Feet of Water (ftH₂O) to Millimeters of Water (mmH₂O) instantly and accurately.
Conversion Formula
mmH₂O = ftH₂O × 304.8
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.
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.
Quick Reference Table
| Feet of Water (ftH₂O) | Millimeters of Water (mmH₂O) |
|---|---|
| 1 ftH₂O | 304.8 mmH₂O |
| 2 ftH₂O | 609.6 mmH₂O |
| 5 ftH₂O | 1524 mmH₂O |
| 10 ftH₂O | 3048 mmH₂O |
| 25 ftH₂O | 7620 mmH₂O |
| 50 ftH₂O | 15240 mmH₂O |
| 100 ftH₂O | 30480 mmH₂O |