To convert inches of water to centimeters of water, multiply by 2.539999898. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
The low-pressure unit for duct static pressure and gas appliances in the US. The unit ventilator and CPAP pressures are set in.
Gauge versus absolute. A tyre gauge reading 32 psi means 32 psi above atmospheric, which is about 46.7 psi absolute. Converting the number is straightforward; remembering which zero it was measured from is where the mistakes happen. N/mm² and MPa are the same size, so a drawing quoting either is quoting the same stress. The tables underneath give both a plain step-by-step lookup and a list of real quantities expressed in centimeters of water, so you can sanity-check whether your answer is a plausible size.
The formula
inches of water- The amount you are converting, in inches of water
2.53999989803- The exact number of centimeters of water in one inch of water
centimeters of water- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 2.53999989803, the exact factor between the two units.
- The answer is shown in centimeters of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A steam boiler: 4010 inH₂O in centimeters of water
A steam boiler comes to about 4010 inH₂O. Multiplying by the factor: 4010 × 2.54 = 10,185.4 cmH₂O. Dividing the answer back by 2.54 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
A domestic water main: 1610 inH₂O in centimeters of water
At 1610 inH₂O (a domestic water main), the same quantity in centimeters of water is 1610 × 2.54 = 4089.4 cmH₂O. One inch of water is 2.54 centimeters of water, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many centimeters of water are in one inch of water?
Exactly 2.53999989803. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert inches of water to centimeters of water?
centimeters of water = inches of water × 2.53999989803. Reversed, inches of water = centimeters of water ÷ 2.53999989803, which is the same as multiplying by 0.393700803207.
Which is the bigger unit, the inch of water or the centimeter of water?
The inch of water. One inch of water equals 2.54 centimeters of water.
What does this quantity actually measure?
Both units measure pressure. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
What is a centimeter of water?
The unit ventilator and CPAP pressures are set in.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do inH₂O to cmH₂O in my head?
Plenty of people do this in their head: multiply by 2.5 instead of using the exact factor 2.539999898. At 100 that shortcut gives 250 centimeters of water, off by 4 centimeters of water or about 1.57%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to centimeters of water reference tables
| Inches Of Water | Centimeters Of Water |
|---|---|
| 0.5 inH₂O | 1.27 cmH₂O |
| 1 inH₂O | 2.54 cmH₂O |
| 2 inH₂O | 5.08 cmH₂O |
| 3 inH₂O | 7.62 cmH₂O |
| 5 inH₂O | 12.7 cmH₂O |
| 10 inH₂O | 25.4 cmH₂O |
| 20 inH₂O | 50.8 cmH₂O |
| 25 inH₂O | 63.5 cmH₂O |
| 50 inH₂O | 127 cmH₂O |
| 75 inH₂O | 190.5 cmH₂O |
| 100 inH₂O | 254 cmH₂O |
| 250 inH₂O | 635 cmH₂O |
| 500 inH₂O | 1270 cmH₂O |
| 1000 inH₂O | 2540 cmH₂O |
| 5000 inH₂O | 12,700 cmH₂O |
Exact factor: 1 inch of water = 2.53999989803 centimeters of water.
| Quantity | inH₂O | cmH₂O |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 1033 cmH₂O |
| A car tyre | 885.8 inH₂O | 2250 cmH₂O |
| Blood pressure, systolic | 64.23 inH₂O | 163.1 cmH₂O |
| A bicycle tyre | 2491 inH₂O | 6328 cmH₂O |
| A domestic water main | 1606 inH₂O | 4079 cmH₂O |
| A steam boiler | 4015 inH₂O | 1.02e+04 cmH₂O |
Published reference values, converted with the same factor this page uses.