One foot of water is exactly 0.02949979669 atmospheres, so converting feet of water to atmospheres 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.
Pump head expressed as a column of water — the way pump curves are drawn. 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
feet of water- The amount you are converting, in feet of water
0.0294997966938- The exact number of atmospheres in one foot of water
atmospheres- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 0.0294997966938, 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: 335 ftH₂O in atmospheres
At 335 ftH₂O (a steam boiler), the same quantity in atmospheres is 335 × 0.0294998 = 9.88243 atm. One foot of water is 0.0294998 atmospheres, so the numbers shrink as expected.
A bicycle tyre: 208 ftH₂O in atmospheres
A bicycle tyre comes to about 208 ftH₂O. Multiplying by the factor: 208 × 0.0294998 = 6.13596 atm. Dividing the answer back by 0.0294998 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 atmospheres are in one foot of water?
Exactly 0.0294997966938. 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 feet of water to atmospheres?
atmospheres = feet of water × 0.0294997966938. Reversed, feet of water = atmospheres ÷ 0.0294997966938, which is the same as multiplying by 33.8985387045.
Which is the bigger unit, the foot of water or the atmosphere?
The atmosphere. One foot of water is only 0.0294998 of a atmosphere, so it takes 33.8985 feet 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 foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
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 ftH₂O to atm in my head?
Plenty of people do this in their head: divide by 34 instead of using the exact factor 0.02949979669. At 100 that shortcut gives 2.9411765 atmospheres, off by 0.008803 atmospheres or about 0.30%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to atmospheres reference tables
| Feet Of Water | Atmospheres |
|---|---|
| 0.5 ftH₂O | 0.0147499 atm |
| 1 ftH₂O | 0.0294998 atm |
| 2 ftH₂O | 0.0589996 atm |
| 3 ftH₂O | 0.0884994 atm |
| 5 ftH₂O | 0.147499 atm |
| 10 ftH₂O | 0.294998 atm |
| 20 ftH₂O | 0.589996 atm |
| 25 ftH₂O | 0.737495 atm |
| 50 ftH₂O | 1.47499 atm |
| 75 ftH₂O | 2.21248 atm |
| 100 ftH₂O | 2.94998 atm |
| 250 ftH₂O | 7.37495 atm |
| 500 ftH₂O | 14.7499 atm |
| 1000 ftH₂O | 29.4998 atm |
| 5000 ftH₂O | 147.499 atm |
Exact factor: 1 foot of water = 0.0294997966938 atmospheres.
| Quantity | ftH₂O | atm |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 1 atm |
| A car tyre | 73.81 ftH₂O | 2.177 atm |
| Blood pressure, systolic | 5.352 ftH₂O | 0.1579 atm |
| A bicycle tyre | 207.6 ftH₂O | 6.124 atm |
| A domestic water main | 133.8 ftH₂O | 3.948 atm |
| A steam boiler | 334.6 ftH₂O | 9.869 atm |
Published reference values, converted with the same factor this page uses.