Convert Hectopascals to Inches of Water
Convert Hectopascals (hPa) to Inches of Water (inH₂O) instantly and accurately.
Conversion Formula
inH₂O = hPa × 0.401463076
About Hectopascals
A hectopascal (hPa) = 100 Pa = 1 mbar - the WMO-official SI-compatible meteorological pressure unit since 1986, replacing millibar with no numerical change. All modern surface observations (METAR, SYNOP), digital barometers, aviation weather, and weather apps report in hPa. QNH altimeter settings outside North America are in hPa. ICAO standard sea-level pressure is 1013.25 hPa. Continental high-pressure record exceeds 1084 hPa; Typhoon Tip (1979) holds the low record at ~870 hPa. 1 hPa = 100 Pa.
About Inches of Water
One inch of water column (inH₂O or in WC) = pressure from 1 inch of fresh water at standard gravity ≈ 249.09 Pa. The standard unit for low-pressure measurement in US HVAC and plumbing: ductwork static pressure, fan performance, filter ratings, and gas appliance manifold pressures are all specified in inches WC. Household natural gas supply pressure is typically 7 in WC (0.25 psi). Blower door tests for building air-tightness use 50 Pa ≈ 0.2 in WC test pressure. 1 inH₂O = 249.089 Pa.
Quick Reference Table
| Hectopascals (hPa) | Inches of Water (inH₂O) |
|---|---|
| 1 hPa | 0.401463 inH₂O |
| 2 hPa | 0.802926 inH₂O |
| 5 hPa | 2.00732 inH₂O |
| 10 hPa | 4.01463 inH₂O |
| 25 hPa | 10.0366 inH₂O |
| 50 hPa | 20.0732 inH₂O |
| 100 hPa | 40.1463 inH₂O |