To convert feet of water to millimeters of mercury, multiply by 22.41984229. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
Pump head expressed as a column of water — the way pump curves are drawn. The clinical unit for blood pressure worldwide.
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 millimeters of mercury, which is usually more useful than the bare number.
The formula
feet of water- The amount you are converting, in feet of water
22.4198422932- The exact number of millimeters of mercury in one foot of water
millimeters of mercury- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 22.4198422932, the exact factor between the two units.
- The answer is shown in millimeters of mercury, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A car tyre: 73.8 ftH₂O in millimeters of mercury
Take a car tyre, roughly 73.8 ftH₂O. The conversion is a single multiplication — 73.8 × 22.4198 — giving 1654.58 mmHg. Because the relationship is proportional, doubling the input doubles the answer to 3309.17 mmHg.
A bicycle tyre: 208 ftH₂O in millimeters of mercury
Take a bicycle tyre, roughly 208 ftH₂O. The conversion is a single multiplication — 208 × 22.4198 — giving 4663.33 mmHg. Because the relationship is proportional, doubling the input doubles the answer to 9326.65 mmHg.
How to read your score
Frequently asked questions
How many millimeters of mercury are in one foot of water?
Exactly 22.4198422932. 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 millimeters of mercury?
millimeters of mercury = feet of water × 22.4198422932. Reversed, feet of water = millimeters of mercury ÷ 22.4198422932, which is the same as multiplying by 0.0446033467551.
Which is the bigger unit, the foot of water or the millimeter of mercury?
The foot of water. One foot of water equals 22.4198 millimeters of mercury.
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 millimeter of mercury?
The clinical unit for blood pressure worldwide.
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 mmHg in my head?
Plenty of people do this in their head: multiply by 22 instead of using the exact factor 22.41984229. At 100 that shortcut gives 2200 millimeters of mercury, off by 41.98 millimeters of mercury or about 1.87%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to millimeters of mercury reference tables
| Feet Of Water | Millimeters Of Mercury |
|---|---|
| 0.5 ftH₂O | 11.2099 mmHg |
| 1 ftH₂O | 22.4198 mmHg |
| 2 ftH₂O | 44.8397 mmHg |
| 3 ftH₂O | 67.2595 mmHg |
| 5 ftH₂O | 112.099 mmHg |
| 10 ftH₂O | 224.198 mmHg |
| 20 ftH₂O | 448.397 mmHg |
| 25 ftH₂O | 560.496 mmHg |
| 50 ftH₂O | 1120.99 mmHg |
| 75 ftH₂O | 1681.49 mmHg |
| 100 ftH₂O | 2241.98 mmHg |
| 250 ftH₂O | 5604.96 mmHg |
| 500 ftH₂O | 11,209.9 mmHg |
| 1000 ftH₂O | 22,419.8 mmHg |
| 5000 ftH₂O | 112,099 mmHg |
Exact factor: 1 foot of water = 22.4198422932 millimeters of mercury.
| Quantity | ftH₂O | mmHg |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 760 mmHg |
| A car tyre | 73.81 ftH₂O | 1655 mmHg |
| Blood pressure, systolic | 5.352 ftH₂O | 120 mmHg |
| A bicycle tyre | 207.6 ftH₂O | 4654 mmHg |
| A domestic water main | 133.8 ftH₂O | 3000 mmHg |
| A steam boiler | 334.6 ftH₂O | 7501 mmHg |
Published reference values, converted with the same factor this page uses.