One inch of mercury is exactly 13.59510199 inches of water, so converting inches of mercury 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.
The low-pressure unit for duct static pressure and gas appliances in the US. US aviation and weather altimeter setting unit.
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 inches of water, which is usually more useful than the bare number.
The formula
inches of mercury- The amount you are converting, in inches of mercury
13.5951019897- The exact number of inches of water in one inch of mercury
inches of water- The converted result
How it works, step by step
- Enter the value in inches of mercury.
- It is multiplied by 13.5951019897, 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 car tyre: 65.2 inHg in inches of water
Take a car tyre, roughly 65.2 inHg. The conversion is a single multiplication — 65.2 × 13.5951 — giving 886.401 inH₂O. Because the relationship is proportional, doubling the input doubles the answer to 1772.8 inH₂O.
A domestic water main: 118 inHg in inches of water
At 118 inHg (a domestic water main), the same quantity in inches of water is 118 × 13.5951 = 1604.22 inH₂O. One inch of mercury is 13.5951 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 inch of mercury?
Exactly 13.5951019897. 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 inches of mercury to inches of water?
inches of water = inches of mercury × 13.5951019897. Reversed, inches of mercury = inches of water ÷ 13.5951019897, which is the same as multiplying by 0.0735559027625.
Which is the bigger unit, the inch of mercury or the inch of water?
The inch of mercury. One inch of mercury equals 13.5951 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 inch of mercury?
US aviation and weather altimeter setting unit.
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 inHg to inH₂O in my head?
Plenty of people do this in their head: multiply by 14 instead of using the exact factor 13.59510199. At 100 that shortcut gives 1400 inches of water, off by 40.49 inches of water or about 2.98%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Mercury to inches of water reference tables
| Inches Of Mercury | Inches Of Water |
|---|---|
| 0.5 inHg | 6.79755 inH₂O |
| 1 inHg | 13.5951 inH₂O |
| 2 inHg | 27.1902 inH₂O |
| 3 inHg | 40.7853 inH₂O |
| 5 inHg | 67.9755 inH₂O |
| 10 inHg | 135.951 inH₂O |
| 20 inHg | 271.902 inH₂O |
| 25 inHg | 339.878 inH₂O |
| 50 inHg | 679.755 inH₂O |
| 75 inHg | 1019.63 inH₂O |
| 100 inHg | 1359.51 inH₂O |
| 250 inHg | 3398.78 inH₂O |
| 500 inHg | 6797.55 inH₂O |
| 1000 inHg | 13,595.1 inH₂O |
| 5000 inHg | 67,975.5 inH₂O |
Exact factor: 1 inch of mercury = 13.5951019897 inches of water.
| Quantity | inHg | inH₂O |
|---|---|---|
| Sea-level air | 29.92 inHg | 406.8 inH₂O |
| A car tyre | 65.15 inHg | 885.8 inH₂O |
| Blood pressure, systolic | 4.724 inHg | 64.23 inH₂O |
| A bicycle tyre | 183.2 inHg | 2491 inH₂O |
| A domestic water main | 118.1 inHg | 1606 inH₂O |
| A steam boiler | 295.3 inHg | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.