Convert Inches of Water to Millibars
Convert Inches of Water (inH₂O) to Millibars (mbar) instantly and accurately.
Conversion Formula
mbar = inH₂O × 2.4908891
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.
About Millibars
A millibar (mbar) = 100 Pa = 1 hPa - the historically dominant meteorological pressure unit. Standard sea-level pressure is 1013.25 mbar. Hurricane intensity is characterised by central pressure: Category 5 storms typically below 920 mbar (US record: 892 mbar, 1935). Upper-air analysis levels - 850, 700, 500, 300, 200 mbar - appear throughout decades of archived meteorological data. Aircraft cabins are pressurised to ~750-800 mbar at cruise altitude. 'Weather bombs' see pressure fall 24+ mbar in 24 hours. 1 mbar = 100 Pa.
Quick Reference Table
| Inches of Water (inH₂O) | Millibars (mbar) |
|---|---|
| 1 inH₂O | 2.49089 mbar |
| 2 inH₂O | 4.98178 mbar |
| 5 inH₂O | 12.4544 mbar |
| 10 inH₂O | 24.9089 mbar |
| 25 inH₂O | 62.2722 mbar |
| 50 inH₂O | 124.544 mbar |
| 100 inH₂O | 249.089 mbar |