Convert Inches of Water to Millibars
1 inch of water (inH₂O) equals 2.4908891 millibars (mbar).
1 inH₂O = 2.4908891 mbar
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk inch of water to millibar converter to paste a column from Excel.
How to Convert Inch of Water to Millibar
- 1 inH₂O = 2.4908891 mbar
- 1 mbar = 0.401463076 inH₂O
- Example: convert 15 inH₂O to mbar: 15 inH₂O = 15 × 2.4908891 mbar = 37.3633365 mbar
Reference conditions. inH₂O: Conventional water column: ρ = 1000 kg/m³ and gₙ = 9.80665 m/s² (≈ water at 4 °C).
Formula
mbar = inH₂O × 2.4908891
Derivation from SI units:
- 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
- 1 mbar = 10⁻³ bar = 100 Pa = 1 hPa
- 1 inH₂O = 249.08891 Pa ÷ 100 Pa per mbar = 2.4908891 mbar
Both units are defined exactly, so the factor is exact. Inch of Water definition: inch of water; Millibar definition: millibar.
Worked examples
- A US gas appliance supplied at 7 inH₂O is at 17.4362237 mbar.
7 inH₂O × 2.4908891 = 17.4362237 mbar - 1 inH₂O equals 2.4908891 mbar.
1 inH₂O × 2.4908891 = 2.4908891 mbar
Inch of Water to Millibar conversion table
| Inches of Water (inH₂O) | Millibars (mbar) |
|---|---|
| 0.01 inH₂O | 0.024908891 mbar |
| 0.02 inH₂O | 0.049817782 mbar |
| 0.03 inH₂O | 0.074726673 mbar |
| 0.05 inH₂O | 0.124544455 mbar |
| 0.1 inH₂O | 0.24908891 mbar |
| 0.15 inH₂O | 0.373633365 mbar |
| 0.2 inH₂O | 0.49817782 mbar |
| 0.25 inH₂O | 0.622722275 mbar |
| 0.3 inH₂O | 0.74726673 mbar |
| 0.4 inH₂O | 0.99635564 mbar |
| 0.5 inH₂O | 1.24544455 mbar |
| 0.75 inH₂O | 1.868166825 mbar |
| 1 inH₂O | 2.4908891 mbar |
| 1.5 inH₂O | 3.73633365 mbar |
| 2 inH₂O | 4.9817782 mbar |
| 2.5 inH₂O | 6.22722275 mbar |
| 3 inH₂O | 7.4726673 mbar |
| 4 inH₂O | 9.9635564 mbar |
| 5 inH₂O | 12.4544455 mbar |
| 7 inH₂O | 17.4362237 mbar |
| 10 inH₂O | 24.908891 mbar |
| 11 inH₂O | 27.3997801 mbar |
| 14 inH₂O | 34.8724474 mbar |
| 20 inH₂O | 49.817782 mbar |
| 27.7 inH₂O | 68.99762807 mbar |
Where it's used
Gas appliances sold in both North America and Europe list supply pressures in inches of water column and in mbar. One inH₂O is about 2.49 mbar.
Inch of Water to other pressure units
| Conversion | 1 inH₂O equals |
|---|---|
| inch of water to pascal | 249.08891 Pa |
| inch of water to kilopascal | 0.24908891 kPa |
| inch of water to megapascal | 0.00024908891 MPa |
| inch of water to psi | 0.036127292 psi |
| inch of water to bar | 0.0024908891 bar |
| inch of water to millibar | 2.4908891 mbar |
| inch of water to decibar | 0.024908891 dbar |
| inch of water to torr | 1.86832047 Torr |
| inch of water to millimeter of mercury | 1.868320204 mmHg |
| inch of water to millimeter of water | 25.4 mmH₂O |
| inch of water to centimeter of water | 2.54 cmH₂O |
| inch of water to inch of water (60 °F) | 1.001000281 inH₂O (60 °F) |
| inch of water to inch of mercury | 0.07355591353 inHg |
| inch of water to atmosphere | 0.002458316408 atm |
| inch of water to barye | 2490.8891 Ba |
Frequently asked questions
What is 20 mbar in inches of water?
20 mbar = 8.029 inH₂O.
How many millibars are in 1 inch of water?
1 inH₂O = 2.4908891 mbar.
How do I convert inches of water to millibars?
Multiply the value in inH₂O by 2.4908891. For example, 15 inH₂O × 2.4908891 = 37.3633365 mbar.
Is the inH₂O to mbar conversion exact?
Yes. Both units are defined exactly, and 1 inH₂O is exactly 2.4908891 mbar.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "inch of water, conventional (inH2O)".
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "millibar".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Inches of Water to Millibars. Retrieved October 17, 2026, from https://scientificconverters.com/pressure/inch-of-water-to-millibar/
IEEE
Scientific Converters, "Convert Inches of Water to Millibars," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/pressure/inch-of-water-to-millibar/