Convert Millimeters of Water to Inches of Water
1 millimeter of water (mmH₂O) equals 0.03937007874 inches of water (inH₂O).
1 mmH₂O = 0.03937007874 inH₂O
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk millimeter of water to inch of water converter to paste a column from Excel.
How to Convert Millimeter of Water to Inch of Water
- 1 mmH₂O = 0.03937007874 inH₂O
- 1 inH₂O = 25.4 mmH₂O
- Example: convert 15 mmH₂O to inH₂O: 15 mmH₂O = 15 × 0.03937007874 inH₂O = 0.5905511811 inH₂O
Reference conditions. mmH₂O: Conventional water column: ρ = 1000 kg/m³ and gₙ = 9.80665 m/s² (≈ water at 4 °C). inH₂O: Conventional water column: ρ = 1000 kg/m³ and gₙ = 9.80665 m/s² (≈ water at 4 °C).
Formula
inH₂O = mmH₂O × 0.03937007874016
or inH₂O = mmH₂O ÷ 25.4
Derivation from SI units:
- 1 mmH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.001 m = 9.80665 Pa
- 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
- 1 mmH₂O = 9.80665 Pa ÷ 249.08891 Pa per inH₂O = 0.03937007874016 inH₂O
Both units are defined exactly, so the factor is exact. Millimeter of Water definition: millimeter of water; Inch of Water definition: inch of water.
Worked examples
- A fan rated 25 mmH₂O has 0.9842519685 inH₂O of static pressure.
25 mmH₂O × 0.03937007874 = 0.9842519685 inH₂O - 10 mmH₂O equals 0.3937007874 inH₂O.
10 mmH₂O × 0.03937007874 = 0.3937007874 inH₂O
Millimeter of Water to Inch of Water conversion table
| Millimeters of Water (mmH₂O) | Inches of Water (inH₂O) |
|---|---|
| 1 mmH₂O | 0.03937007874 inH₂O |
| 2 mmH₂O | 0.07874015748 inH₂O |
| 5 mmH₂O | 0.1968503937 inH₂O |
| 10 mmH₂O | 0.3937007874 inH₂O |
| 15 mmH₂O | 0.5905511811 inH₂O |
| 20 mmH₂O | 0.7874015748 inH₂O |
| 25 mmH₂O | 0.9842519685 inH₂O |
| 30 mmH₂O | 1.181102362 inH₂O |
| 50 mmH₂O | 1.968503937 inH₂O |
| 75 mmH₂O | 2.952755906 inH₂O |
| 100 mmH₂O | 3.937007874 inH₂O |
| 150 mmH₂O | 5.905511811 inH₂O |
| 200 mmH₂O | 7.874015748 inH₂O |
| 250 mmH₂O | 9.842519685 inH₂O |
| 300 mmH₂O | 11.81102362 inH₂O |
| 500 mmH₂O | 19.68503937 inH₂O |
| 1000 mmH₂O | 39.37007874 inH₂O |
| 2000 mmH₂O | 78.74015748 inH₂O |
| 5000 mmH₂O | 196.8503937 inH₂O |
| 10000 mmH₂O | 393.7007874 inH₂O |
Where it's used
Fans and filters specified in mmAq on Asian datasheets are converted to inches of water for US projects and controls.
Millimeter of Water to other pressure units
| Conversion | 1 mmH₂O equals |
|---|---|
| millimeter of water to pascal | 9.80665 Pa |
| millimeter of water to kilopascal | 0.00980665 kPa |
| millimeter of water to megapascal | 0.00000980665 MPa |
| millimeter of water to psi | 0.001422334331 psi |
| millimeter of water to bar | 0.0000980665 bar |
| millimeter of water to millibar | 0.0980665 mbar |
| millimeter of water to decibar | 0.000980665 dbar |
| millimeter of water to torr | 0.07355592401 Torr |
| millimeter of water to millimeter of mercury | 0.07355591353 mmHg |
| millimeter of water to centimeter of water | 0.1 cmH₂O |
| millimeter of water to inch of water | 0.03937007874 inH₂O |
| millimeter of water to inch of water (60 °F) | 0.03940945989 inH₂O (60 °F) |
| millimeter of water to inch of mercury | 0.002895902107 inHg |
| millimeter of water to atmosphere | 0.00009678411054 atm |
| millimeter of water to barye | 98.0665 Ba |
Frequently asked questions
How do I convert mmAq to in WC?
Divide by 25.4: 50 mmAq = 1.969 inH₂O.
How many inches of water are in 1 millimeter of water?
1 mmH₂O = 0.03937007874 inH₂O.
How do I convert millimeters of water to inches of water?
Multiply the value in mmH₂O by 0.03937007874, or divide it by 25.4. For example, 15 mmH₂O × 0.03937007874 = 0.5905511811 inH₂O.
Is the mmH₂O to inH₂O conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
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, "millimeter of water, conventional (mmH2O)".
- 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)".
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 Millimeters of Water to Inches of Water. Retrieved October 17, 2026, from https://scientificconverters.com/pressure/millimeter-of-water-to-inch-of-water/
IEEE
Scientific Converters, "Convert Millimeters of Water to Inches of Water," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/pressure/millimeter-of-water-to-inch-of-water/