One centimeter of water is exactly 0.3937008032 inches of water, so converting centimeters of water to inches of water is a single multiplication. Enter any figure and the result appears as you type — the arithmetic runs in your browser, so nothing is sent anywhere.
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 inches of water, so you can sanity-check whether your answer is a plausible size.
The formula
centimeters of water- The amount you are converting, in centimeters of water
0.393700803207- The exact number of inches of water in one centimeter of water
inches of water- The converted result
How it works, step by step
- Enter the value in centimeters of water.
- It is multiplied by 0.393700803207, the exact factor between the two units.
- The answer is shown in inches of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Blood pressure, systolic: 163 cmH₂O in inches of water
At 163 cmH₂O (blood pressure, systolic), the same quantity in inches of water is 163 × 0.393701 = 64.1732 inH₂O. One centimeter of water is 0.393701 inches of water, so the numbers shrink as expected.
A domestic water main: 4080 cmH₂O in inches of water
A domestic water main comes to about 4080 cmH₂O. Multiplying by the factor: 4080 × 0.393701 = 1606.3 inH₂O. Dividing the answer back by 0.393701 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
How to read your score
Frequently asked questions
How many inches of water are in one centimeter of water?
Exactly 0.393700803207. 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 centimeters of water to inches of water?
inches of water = centimeters of water × 0.393700803207. Reversed, centimeters of water = inches of water ÷ 0.393700803207, which is the same as multiplying by 2.53999989803.
Which is the bigger unit, the centimeter of water or the inch of water?
The inch of water. One centimeter of water is only 0.393701 of a inch of water, so it takes 2.54 centimeters of water to make one inch 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 centimeter of water?
The unit ventilator and CPAP pressures are set in.
What is a inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
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 cmH₂O to inH₂O in my head?
Plenty of people do this in their head: divide by 2.5 instead of using the exact factor 0.3937008032. At 100 that shortcut gives 40 inches of water, off by 0.6299 inches of water or about 1.60%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Centimeters Of Water to inches of water reference tables
| Centimeters Of Water | Inches Of Water |
|---|---|
| 0.5 cmH₂O | 0.19685 inH₂O |
| 1 cmH₂O | 0.393701 inH₂O |
| 2 cmH₂O | 0.787402 inH₂O |
| 3 cmH₂O | 1.1811 inH₂O |
| 5 cmH₂O | 1.9685 inH₂O |
| 10 cmH₂O | 3.93701 inH₂O |
| 20 cmH₂O | 7.87402 inH₂O |
| 25 cmH₂O | 9.84252 inH₂O |
| 50 cmH₂O | 19.685 inH₂O |
| 75 cmH₂O | 29.5276 inH₂O |
| 100 cmH₂O | 39.3701 inH₂O |
| 250 cmH₂O | 98.4252 inH₂O |
| 500 cmH₂O | 196.85 inH₂O |
| 1000 cmH₂O | 393.701 inH₂O |
| 5000 cmH₂O | 1968.5 inH₂O |
Exact factor: 1 centimeter of water = 0.393700803207 inches of water.
| Quantity | cmH₂O | inH₂O |
|---|---|---|
| Sea-level air | 1033 cmH₂O | 406.8 inH₂O |
| A car tyre | 2250 cmH₂O | 885.8 inH₂O |
| Blood pressure, systolic | 163.1 cmH₂O | 64.23 inH₂O |
| A bicycle tyre | 6328 cmH₂O | 2491 inH₂O |
| A domestic water main | 4079 cmH₂O | 1606 inH₂O |
| A steam boiler | 1.02e+04 cmH₂O | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.