One foot of water is exactly 22,419.84549 millitorr, so converting feet of water to millitorr 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. One thousandth of a torr, the working unit of vacuum deposition.
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 millitorr 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
22,419.8454873- The exact number of millitorr in one foot of water
millitorr- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 22,419.8454873, the exact factor between the two units.
- The answer is shown in millitorr, 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 millitorr
At 335 ftH₂O (a steam boiler), the same quantity in millitorr is 335 × 22,419.8 = 7.51065e+06 mTorr. One foot of water is 22,419.8 millitorr, so the numbers grow as expected.
Blood pressure, systolic: 5.35 ftH₂O in millitorr
At 5.35 ftH₂O (blood pressure, systolic), the same quantity in millitorr is 5.35 × 22,419.8 = 119,946 mTorr. One foot of water is 22,419.8 millitorr, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many millitorr are in one foot of water?
Exactly 22,419.8454873. 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 millitorr?
millitorr = feet of water × 22,419.8454873. Reversed, feet of water = millitorr ÷ 22,419.8454873, which is the same as multiplying by 4.46033404007e-05.
Which is the bigger unit, the foot of water or the millitorr?
The foot of water. One foot of water equals 22,419.8 millitorr.
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 millitorr?
One thousandth of a torr, the working unit of vacuum deposition.
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 mTorr in my head?
Plenty of people do this in their head: multiply by 22,000 instead of using the exact factor 22,419.84549. At 100 that shortcut gives 2,200,000 millitorr, off by 41984.548729 millitorr or about 1.87%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to millitorr reference tables
| Feet Of Water | Millitorr |
|---|---|
| 0.5 ftH₂O | 11,209.9 mTorr |
| 1 ftH₂O | 22,419.8 mTorr |
| 2 ftH₂O | 44,839.7 mTorr |
| 3 ftH₂O | 67,259.5 mTorr |
| 5 ftH₂O | 112,099 mTorr |
| 10 ftH₂O | 224,198 mTorr |
| 20 ftH₂O | 448,397 mTorr |
| 25 ftH₂O | 560,496 mTorr |
| 50 ftH₂O | 1.12099e+06 mTorr |
| 75 ftH₂O | 1.68149e+06 mTorr |
| 100 ftH₂O | 2.24198e+06 mTorr |
| 250 ftH₂O | 5.60496e+06 mTorr |
| 500 ftH₂O | 1.12099e+07 mTorr |
| 1000 ftH₂O | 2.24198e+07 mTorr |
| 5000 ftH₂O | 1.12099e+08 mTorr |
Exact factor: 1 foot of water = 22,419.8454873 millitorr.
| Quantity | ftH₂O | mTorr |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 7.6e+05 mTorr |
| A car tyre | 73.81 ftH₂O | 1.655e+06 mTorr |
| Blood pressure, systolic | 5.352 ftH₂O | 1.2e+05 mTorr |
| A bicycle tyre | 207.6 ftH₂O | 4.654e+06 mTorr |
| A domestic water main | 133.8 ftH₂O | 3e+06 mTorr |
| A steam boiler | 334.6 ftH₂O | 7.501e+06 mTorr |
Published reference values, converted with the same factor this page uses.