One henry is exactly 1000 millihenries, so converting henries to millihenries 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.
Millihenries cover audio crossovers, relay coils and the smoothing chokes in linear supplies. The henry is the SI unit of inductance: one volt induced per amp-per-second change in current.
Two tables follow: rounded steps for quick lookup, and a set of real reference quantities converted into millihenries, which is usually more useful than the bare number.
The formula
henries- The amount you are converting, in henries
1000- The exact number of millihenries in one henry
millihenries- The converted result
How it works, step by step
- Enter the value in henries.
- It is multiplied by 1000, the exact factor between the two units.
- The answer is shown in millihenries, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Mains transformer primary: 5 H in millihenries
Take mains transformer primary, roughly 5 H. The conversion is a single multiplication — 5 × 1000 — giving 5000 mH. Because the relationship is proportional, doubling the input doubles the answer to 10,000 mH.
Relay coil: 0.1 H in millihenries
Relay coil comes to about 0.1 H. Multiplying by the factor: 0.1 × 1000 = 100 mH. Dividing the answer back by 1000 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
How to read your score
Frequently asked questions
How many millihenries are in one henry?
Exactly 1000. 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 henries to millihenries?
millihenries = henries × 1000. Reversed, henries = millihenries ÷ 1000, which is the same as multiplying by 0.001.
Which is the bigger unit, the henry or the millihenry?
The henry. One henry equals 1000 millihenries.
What does this quantity actually measure?
Both units measure how strongly a coil opposes a change in current. 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 henry?
The henry is the SI unit of inductance: one volt induced per amp-per-second change in current.
What is a millihenry?
Millihenries cover audio crossovers, relay coils and the smoothing chokes in linear supplies.
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.
Henries to millihenries reference tables
| Henries | Millihenries |
|---|---|
| 0.5 H | 500 mH |
| 1 H | 1000 mH |
| 2 H | 2000 mH |
| 3 H | 3000 mH |
| 5 H | 5000 mH |
| 10 H | 10,000 mH |
| 20 H | 20,000 mH |
| 25 H | 25,000 mH |
| 50 H | 50,000 mH |
| 75 H | 75,000 mH |
| 100 H | 100,000 mH |
| 250 H | 250,000 mH |
| 500 H | 500,000 mH |
| 1000 H | 1e+06 mH |
| 5000 H | 5e+06 mH |
Exact factor: 1 henry = 1000 millihenries.
| Quantity | H | mH |
|---|---|---|
| PCB trace, 25 mm | 2e-08 H | 2e-05 mH |
| RF choke | 1e-05 H | 0.01 mH |
| Buck converter inductor | 4.7e-05 H | 0.047 mH |
| Speaker crossover coil | 0.0015 H | 1.5 mH |
| Relay coil | 0.1 H | 100 mH |
| Mains transformer primary | 5 H | 5000 mH |
Published reference values, converted with the same factor this page uses.