One foot of water is exactly 12.0000004 inches of water, so converting feet 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.
Pump head expressed as a column of water — the way pump curves are drawn. The low-pressure unit for duct static pressure and gas appliances in the US.
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 inches of water so the number you get has something to be compared against.
The formula
feet of water- The amount you are converting, in feet of water
12.0000004015- The exact number of inches of water in one foot of water
inches of water- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 12.0000004015, 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
A bicycle tyre: 208 ftH₂O in inches of water
A bicycle tyre comes to about 208 ftH₂O. Multiplying by the factor: 208 × 12 = 2496 inH₂O. Dividing the answer back by 12 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
Sea-level air: 33.9 ftH₂O in inches of water
At 33.9 ftH₂O (sea-level air), the same quantity in inches of water is 33.9 × 12 = 406.8 inH₂O. One foot of water is 12 inches of water, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many inches of water are in one foot of water?
Exactly 12.0000004015. 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 inches of water?
inches of water = feet of water × 12.0000004015. Reversed, feet of water = inches of water ÷ 12.0000004015, which is the same as multiplying by 0.0833333305454.
Which is the bigger unit, the foot of water or the inch of water?
The foot of water. One foot of water equals 12 inches 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 foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
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 ftH₂O to inH₂O in my head?
Plenty of people do this in their head: multiply by 12 instead of using the exact factor 12.0000004. At 100 that shortcut gives 1200 inches of water, off by 0.000040 inches of water or about 0.00%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to inches of water reference tables
| Feet Of Water | Inches Of Water |
|---|---|
| 0.5 ftH₂O | 6 inH₂O |
| 1 ftH₂O | 12 inH₂O |
| 2 ftH₂O | 24 inH₂O |
| 3 ftH₂O | 36 inH₂O |
| 5 ftH₂O | 60 inH₂O |
| 10 ftH₂O | 120 inH₂O |
| 20 ftH₂O | 240 inH₂O |
| 25 ftH₂O | 300 inH₂O |
| 50 ftH₂O | 600 inH₂O |
| 75 ftH₂O | 900 inH₂O |
| 100 ftH₂O | 1200 inH₂O |
| 250 ftH₂O | 3000 inH₂O |
| 500 ftH₂O | 6000 inH₂O |
| 1000 ftH₂O | 12,000 inH₂O |
| 5000 ftH₂O | 60,000 inH₂O |
Exact factor: 1 foot of water = 12.0000004015 inches of water.
| Quantity | ftH₂O | inH₂O |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 406.8 inH₂O |
| A car tyre | 73.81 ftH₂O | 885.8 inH₂O |
| Blood pressure, systolic | 5.352 ftH₂O | 64.23 inH₂O |
| A bicycle tyre | 207.6 ftH₂O | 2491 inH₂O |
| A domestic water main | 133.8 ftH₂O | 1606 inH₂O |
| A steam boiler | 334.6 ftH₂O | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.