This page converts inches of mercury into millitorr using the factor 25,400.00632, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
US aviation and weather altimeter setting unit. 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. Two tables follow: rounded steps for quick lookup, and a set of real reference quantities converted into millitorr, which is usually more useful than the bare number.
The formula
inches of mercury- The amount you are converting, in inches of mercury
25,400.0063163- The exact number of millitorr in one inch of mercury
millitorr- The converted result
How it works, step by step
- Enter the value in inches of mercury.
- It is multiplied by 25,400.0063163, 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 car tyre: 65.2 inHg in millitorr
Take a car tyre, roughly 65.2 inHg. The conversion is a single multiplication — 65.2 × 25,400 — giving 1.65608e+06 mTorr. Because the relationship is proportional, doubling the input doubles the answer to 3.31216e+06 mTorr.
A steam boiler: 295 inHg in millitorr
At 295 inHg (a steam boiler), the same quantity in millitorr is 295 × 25,400 = 7.493e+06 mTorr. One inch of mercury is 25,400 millitorr, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many millitorr are in one inch of mercury?
Exactly 25,400.0063163. 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 millitorr?
millitorr = inches of mercury × 25,400.0063163. Reversed, inches of mercury = millitorr ÷ 25,400.0063163, which is the same as multiplying by 3.93700689499e-05.
Which is the bigger unit, the inch of mercury or the millitorr?
The inch of mercury. One inch of mercury equals 25,400 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 inch of mercury?
US aviation and weather altimeter setting unit.
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 inHg to mTorr in my head?
Plenty of people do this in their head: multiply by 25,000 instead of using the exact factor 25,400.00632. At 100 that shortcut gives 2,500,000 millitorr, off by 40000.631631 millitorr or about 1.57%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Mercury to millitorr reference tables
| Inches Of Mercury | Millitorr |
|---|---|
| 0.5 inHg | 12,700 mTorr |
| 1 inHg | 25,400 mTorr |
| 2 inHg | 50,800 mTorr |
| 3 inHg | 76,200 mTorr |
| 5 inHg | 127,000 mTorr |
| 10 inHg | 254,000 mTorr |
| 20 inHg | 508,000 mTorr |
| 25 inHg | 635,000 mTorr |
| 50 inHg | 1.27e+06 mTorr |
| 75 inHg | 1.905e+06 mTorr |
| 100 inHg | 2.54e+06 mTorr |
| 250 inHg | 6.35e+06 mTorr |
| 500 inHg | 1.27e+07 mTorr |
| 1000 inHg | 2.54e+07 mTorr |
| 5000 inHg | 1.27e+08 mTorr |
Exact factor: 1 inch of mercury = 25,400.0063163 millitorr.
| Quantity | inHg | mTorr |
|---|---|---|
| Sea-level air | 29.92 inHg | 7.6e+05 mTorr |
| A car tyre | 65.15 inHg | 1.655e+06 mTorr |
| Blood pressure, systolic | 4.724 inHg | 1.2e+05 mTorr |
| A bicycle tyre | 183.2 inHg | 4.654e+06 mTorr |
| A domestic water main | 118.1 inHg | 3e+06 mTorr |
| A steam boiler | 295.3 inHg | 7.501e+06 mTorr |
Published reference values, converted with the same factor this page uses.