One atmosphere is exactly 1033.227453 centimeters of water, so converting atmospheres to centimeters 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.
Standard atmospheric pressure by definition — 101,325 pascals exactly. 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. Below the calculator there is a step table for the values people look up most, and a second table putting real pressure figures into centimeters of water so the number you get has something to be compared against.
The formula
atmospheres- The amount you are converting, in atmospheres
1033.2274528- The exact number of centimeters of water in one atmosphere
centimeters of water- The converted result
How it works, step by step
- Enter the value in atmospheres.
- It is multiplied by 1033.2274528, 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 car tyre: 2.18 atm in centimeters of water
At 2.18 atm (a car tyre), the same quantity in centimeters of water is 2.18 × 1033.23 = 2252.44 cmH₂O. One atmosphere is 1033.23 centimeters of water, so the numbers grow as expected.
A bicycle tyre: 6.12 atm in centimeters of water
A bicycle tyre comes to about 6.12 atm. Multiplying by the factor: 6.12 × 1033.23 = 6323.35 cmH₂O. Dividing the answer back by 1033.23 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 centimeters of water are in one atmosphere?
Exactly 1033.2274528. 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 atmospheres to centimeters of water?
centimeters of water = atmospheres × 1033.2274528. Reversed, atmospheres = centimeters of water ÷ 1033.2274528, which is the same as multiplying by 0.000967841105354.
Which is the bigger unit, the atmosphere or the centimeter of water?
The atmosphere. One atmosphere equals 1033.23 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 atmosphere?
Standard atmospheric pressure by definition — 101,325 pascals exactly.
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 atm to cmH₂O in my head?
Plenty of people do this in their head: multiply by 1000 instead of using the exact factor 1033.227453. At 100 that shortcut gives 100,000 centimeters of water, off by 3323 centimeters of water or about 3.22%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Atmospheres to centimeters of water reference tables
| Atmospheres | Centimeters Of Water |
|---|---|
| 0.5 atm | 516.614 cmH₂O |
| 1 atm | 1033.23 cmH₂O |
| 2 atm | 2066.45 cmH₂O |
| 3 atm | 3099.68 cmH₂O |
| 5 atm | 5166.14 cmH₂O |
| 10 atm | 10,332.3 cmH₂O |
| 20 atm | 20,664.5 cmH₂O |
| 25 atm | 25,830.7 cmH₂O |
| 50 atm | 51,661.4 cmH₂O |
| 75 atm | 77,492.1 cmH₂O |
| 100 atm | 103,323 cmH₂O |
| 250 atm | 258,307 cmH₂O |
| 500 atm | 516,614 cmH₂O |
| 1000 atm | 1.03323e+06 cmH₂O |
| 5000 atm | 5.16614e+06 cmH₂O |
Exact factor: 1 atmosphere = 1033.2274528 centimeters of water.
| Quantity | atm | cmH₂O |
|---|---|---|
| Sea-level air | 1 atm | 1033 cmH₂O |
| A car tyre | 2.177 atm | 2250 cmH₂O |
| Blood pressure, systolic | 0.1579 atm | 163.1 cmH₂O |
| A bicycle tyre | 6.124 atm | 6328 cmH₂O |
| A domestic water main | 3.948 atm | 4079 cmH₂O |
| A steam boiler | 9.869 atm | 1.02e+04 cmH₂O |
Published reference values, converted with the same factor this page uses.