One atmosphere is exactly 33.8985387 feet of water, so converting atmospheres to feet 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. Pump head expressed as a column of water — the way pump curves are drawn.
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. Two tables follow: rounded steps for quick lookup, and a set of real reference quantities converted into feet of water, which is usually more useful than the bare number.
The formula
atmospheres- The amount you are converting, in atmospheres
33.8985387045- The exact number of feet of water in one atmosphere
feet of water- The converted result
How it works, step by step
- Enter the value in atmospheres.
- It is multiplied by 33.8985387045, the exact factor between the two units.
- The answer is shown in feet of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A bicycle tyre: 6.12 atm in feet of water
At 6.12 atm (a bicycle tyre), the same quantity in feet of water is 6.12 × 33.8985 = 207.459 ftH₂O. One atmosphere is 33.8985 feet of water, so the numbers grow as expected.
A steam boiler: 9.87 atm in feet of water
A steam boiler comes to about 9.87 atm. Multiplying by the factor: 9.87 × 33.8985 = 334.579 ftH₂O. Dividing the answer back by 33.8985 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 feet of water are in one atmosphere?
Exactly 33.8985387045. 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 feet of water?
feet of water = atmospheres × 33.8985387045. Reversed, atmospheres = feet of water ÷ 33.8985387045, which is the same as multiplying by 0.0294997966938.
Which is the bigger unit, the atmosphere or the foot of water?
The atmosphere. One atmosphere equals 33.8985 feet 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 foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
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 ftH₂O in my head?
Plenty of people do this in their head: multiply by 34 instead of using the exact factor 33.8985387. At 100 that shortcut gives 3400 feet of water, off by 10.15 feet of water or about 0.30%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Atmospheres to feet of water reference tables
| Atmospheres | Feet Of Water |
|---|---|
| 0.5 atm | 16.9493 ftH₂O |
| 1 atm | 33.8985 ftH₂O |
| 2 atm | 67.7971 ftH₂O |
| 3 atm | 101.696 ftH₂O |
| 5 atm | 169.493 ftH₂O |
| 10 atm | 338.985 ftH₂O |
| 20 atm | 677.971 ftH₂O |
| 25 atm | 847.463 ftH₂O |
| 50 atm | 1694.93 ftH₂O |
| 75 atm | 2542.39 ftH₂O |
| 100 atm | 3389.85 ftH₂O |
| 250 atm | 8474.63 ftH₂O |
| 500 atm | 16,949.3 ftH₂O |
| 1000 atm | 33,898.5 ftH₂O |
| 5000 atm | 169,493 ftH₂O |
Exact factor: 1 atmosphere = 33.8985387045 feet of water.
| Quantity | atm | ftH₂O |
|---|---|---|
| Sea-level air | 1 atm | 33.9 ftH₂O |
| A car tyre | 2.177 atm | 73.81 ftH₂O |
| Blood pressure, systolic | 0.1579 atm | 5.352 ftH₂O |
| A bicycle tyre | 6.124 atm | 207.6 ftH₂O |
| A domestic water main | 3.948 atm | 133.8 ftH₂O |
| A steam boiler | 9.869 atm | 334.6 ftH₂O |
Published reference values, converted with the same factor this page uses.