Mils to Millimeters Converter

How it is calculated

The converter uses the exact factor 1 mil = 0.0254 mm, because a mil is 1/1000 inch and an inch is 25.4 mm. Mils to millimetres: mm = mil × 0.0254. Millimetres to mils: mil = mm ÷ 0.0254, which is the same as multiplying by about 39.3701. Choose the direction first, then type the number; the result is rounded to four decimal places and the original value is echoed back in the other unit as a check. Negative values are not accepted and give no result. Here “mil” means a thousandth of an inch, not a millimetre and not the Roman-numeral thousand.

Common mistakes

• Confusing mil with mm. A “10 mil” trace is about 0.25 mm; reading it as 10 mm makes it 40 times too wide.
• Leaving the direction on mils to mm while typing a millimetre value, so the answer is 39 times too small.
• Mixing up mil (thousandth of an inch) with “mil” used in the US for a circular mil in wire sizing, or with the military-spec “MIL” prefix.
• Typing a negative value for a tolerance such as −2 mil. The tool returns nothing for negatives; convert the magnitude and apply the sign yourself.
• Rounding the four-decimal result too early on tight tolerances; keep the full 0.0254 factor until the final step.