One millimeter is exactly 4.970969538e-05 chains, so converting millimeters to chains 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.
One thousandth of a metre — the finest gradation on a standard ruler. Sixty-six feet — the length of a cricket pitch, and the unit the US Public Land Survey was laid out in.
The mil and the millimetre are not the same thing and are out by a factor of about forty. A mil is one thousandth of an inch — 0.0254 mm — and a spec sheet that quotes film thickness in mils means the small unit. British drawings write the same size as "thou". Two tables follow: rounded steps for quick lookup, and a set of real reference quantities converted into chains, which is usually more useful than the bare number.
The formula
millimeters- The amount you are converting, in millimeters
4.9709695379e-05- The exact number of chains in one millimeter
chains- The converted result
How it works, step by step
- Enter the value in millimeters.
- It is multiplied by 4.9709695379e-05, the exact factor between the two units.
- The answer is shown in chains, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
The Eiffel Tower: 3.3e+05 mm in chains
At 3.3e+05 mm (the eiffel tower), the same quantity in chains is 3.3e+05 × 4.97097e-05 = 16.4042 ch. One millimeter is 4.97097e-05 chains, so the numbers shrink as expected.
A credit card’s long edge: 85.6 mm in chains
A credit card’s long edge comes to about 85.6 mm. Multiplying by the factor: 85.6 × 4.97097e-05 = 0.00425515 ch. Dividing the answer back by 4.97097e-05 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 chains are in one millimeter?
Exactly 4.9709695379e-05. 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 millimeters to chains?
chains = millimeters × 4.9709695379e-05. Reversed, millimeters = chains ÷ 4.9709695379e-05, which is the same as multiplying by 20,116.8.
Which is the bigger unit, the millimeter or the chain?
The chain. One millimeter is only 4.97097e-05 of a chain, so it takes 20,116.8 millimeters to make one chain.
What does this quantity actually measure?
Both units measure length. 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 millimeter?
One thousandth of a metre — the finest gradation on a standard ruler.
What is a chain?
Sixty-six feet — the length of a cricket pitch, and the unit the US Public Land Survey was laid out in.
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 mm to ch in my head?
Plenty of people do this in their head: divide by 20,000 instead of using the exact factor 0.000050. At 100 that shortcut gives 0.005 chains, off by 0.000029 chains or about 0.58%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Millimeters to chains reference tables
| Millimeters | Chains |
|---|---|
| 0.5 mm | 2.48548e-05 ch |
| 1 mm | 4.97097e-05 ch |
| 2 mm | 9.94194e-05 ch |
| 3 mm | 0.000149129 ch |
| 5 mm | 0.000248548 ch |
| 10 mm | 0.000497097 ch |
| 20 mm | 0.000994194 ch |
| 25 mm | 0.00124274 ch |
| 50 mm | 0.00248548 ch |
| 75 mm | 0.00372823 ch |
| 100 mm | 0.00497097 ch |
| 250 mm | 0.0124274 ch |
| 500 mm | 0.0248548 ch |
| 1000 mm | 0.0497097 ch |
| 5000 mm | 0.248548 ch |
Exact factor: 1 millimeter = 4.9709695379e-05 chains.
| Quantity | mm | ch |
|---|---|---|
| A credit card’s long edge | 85.6 mm | 0.004255 ch |
| A door height | 2032 mm | 0.101 ch |
| An Olympic pool | 5e+04 mm | 2.485 ch |
| The Eiffel Tower | 3.3e+05 mm | 16.4 ch |
| A marathon | 4.22e+07 mm | 2098 ch |
| Earth’s diameter | 1.274e+10 mm | 6.334e+05 ch |
Published reference values, converted with the same factor this page uses.