To convert centimeters of water to atmospheres, multiply by 0.0009678411054. 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 unit ventilator and CPAP pressures are set in. Standard atmospheric pressure by definition — 101,325 pascals exactly.
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 atmospheres, 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
0.000967841105354- The exact number of atmospheres in one centimeter of water
atmospheres- The converted result
How it works, step by step
- Enter the value in centimeters of water.
- It is multiplied by 0.000967841105354, the exact factor between the two units.
- The answer is shown in atmospheres, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A steam boiler: 1.02e+04 cmH₂O in atmospheres
At 1.02e+04 cmH₂O (a steam boiler), the same quantity in atmospheres is 1.02e+04 × 0.000967841 = 9.87198 atm. One centimeter of water is 0.000967841 atmospheres, so the numbers shrink as expected.
A car tyre: 2250 cmH₂O in atmospheres
At 2250 cmH₂O (a car tyre), the same quantity in atmospheres is 2250 × 0.000967841 = 2.17764 atm. One centimeter of water is 0.000967841 atmospheres, so the numbers shrink as expected.
How to read your score
Frequently asked questions
How many atmospheres are in one centimeter of water?
Exactly 0.000967841105354. 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 atmospheres?
atmospheres = centimeters of water × 0.000967841105354. Reversed, centimeters of water = atmospheres ÷ 0.000967841105354, which is the same as multiplying by 1033.2274528.
Which is the bigger unit, the centimeter of water or the atmosphere?
The atmosphere. One centimeter of water is only 0.000967841 of a atmosphere, so it takes 1033.23 centimeters of water to make one atmosphere.
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 atmosphere?
Standard atmospheric pressure by definition — 101,325 pascals exactly.
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 atm in my head?
Plenty of people do this in their head: divide by 1000 instead of using the exact factor 0.0009678411054. At 100 that shortcut gives 0.1 atmospheres, off by 0.003216 atmospheres or about 3.32%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Centimeters Of Water to atmospheres reference tables
| Centimeters Of Water | Atmospheres |
|---|---|
| 0.5 cmH₂O | 0.000483921 atm |
| 1 cmH₂O | 0.000967841 atm |
| 2 cmH₂O | 0.00193568 atm |
| 3 cmH₂O | 0.00290352 atm |
| 5 cmH₂O | 0.00483921 atm |
| 10 cmH₂O | 0.00967841 atm |
| 20 cmH₂O | 0.0193568 atm |
| 25 cmH₂O | 0.024196 atm |
| 50 cmH₂O | 0.0483921 atm |
| 75 cmH₂O | 0.0725881 atm |
| 100 cmH₂O | 0.0967841 atm |
| 250 cmH₂O | 0.24196 atm |
| 500 cmH₂O | 0.483921 atm |
| 1000 cmH₂O | 0.967841 atm |
| 5000 cmH₂O | 4.83921 atm |
Exact factor: 1 centimeter of water = 0.000967841105354 atmospheres.
| Quantity | cmH₂O | atm |
|---|---|---|
| Sea-level air | 1033 cmH₂O | 1 atm |
| A car tyre | 2250 cmH₂O | 2.177 atm |
| Blood pressure, systolic | 163.1 cmH₂O | 0.1579 atm |
| A bicycle tyre | 6328 cmH₂O | 6.124 atm |
| A domestic water main | 4079 cmH₂O | 3.948 atm |
| A steam boiler | 1.02e+04 cmH₂O | 9.869 atm |
Published reference values, converted with the same factor this page uses.