Mil to mm Conversion Calculator — Thou to Millimeters
Convert mils (thousandths of an inch) to millimeters, micrometers, centimeters and inches. The conversion is exact: 1 mil = 0.0254 mm = 25.4 µm, derived from the definition 1 inch = 25.4 mm.
mil
Exact conversion: 1 mil = 0.0254 mm
- 1
Conversion factor
1 mil = 25.4 mm ÷ 1,000 = 0.0254Since 1 inch = 25.4 mm exactly, 1 mil = 0.001 in = 0.0254 mm. - 2
Convert mils to mm
100 × 0.0254 = 2.540000
How does this calculator work?
Multiply mils by 0.0254 to get millimeters, or by 25.4 to get micrometers. Both conversions are exact. Common examples: 1 mil = 0.0254 mm = 25.4 µm; 6 mil PCB trace = 0.1524 mm; 100 mils = 2.54 mm. To reverse, divide mm by 0.0254 to get mils.
Formula
How this is calculated
A mil (thousandth of an inch, also called a thou) is defined as exactly 1/1000 of an inch. Since 1 inch = 25.4 mm exactly (by international agreement since 1959), 1 mil = 0.001 × 25.4 mm = 0.0254 mm = 25.4 µm. All these conversions are exact — there is no rounding involved.
The unit is widely used in precision manufacturing and electronics. PCB trace widths and clearances are typically specified in mils in North American EDA tools (for example, a 6 mil trace = 6 × 0.0254 = 0.1524 mm). Industrial paint and powder-coat dry-film thickness gauges read in mils. Sheet metal and foil gauges in the US are also often quoted in mils, while the rest of the world uses micrometers for the same scales.
This calculator also shows micrometers (µm) prominently because the µm is the natural metric counterpart for the mil scale — many international datasheets give values in µm that engineers then need to compare with mil-based specifications. To convert from mm back to mils, divide by 0.0254, which is equivalent to multiplying by 39.3701.
Frequently asked questions
Multiply the number of mils by 0.0254 to get millimeters. This is exact: 1 mil = 0.001 in, and 1 in = 25.4 mm, so 1 mil = 0.0254 mm. For example, 6 mils × 0.0254 = 0.1524 mm.
1 mm = 1 ÷ 0.0254 ≈ 39.37 mils. Equivalently, 1 mm ≈ 39.37 thou. This is useful when converting metric datasheet values back to mils for PCB layout software.
A mil (thou) is 1/1000 of an inch = 0.0254 mm. A millimeter is much larger — 1 mm ≈ 39.37 mils. Despite the similar-sounding names, they differ by a factor of about 39. Always check context: in US manufacturing 'mil' usually means thou; in European documents it almost always means millimeter.
Also known as
TG we-Calculate Editorial Team. (2026). Mil to mm Conversion Calculator — Thou to Millimeters [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/mil-to-mm-conversion-calculator
TG we-Calculate Editorial Team. "Mil to mm Conversion Calculator — Thou to Millimeters." TG we-Calculate. 2026. https://we-calculate.com/calculator/mil-to-mm-conversion-calculator.
TG we-Calculate Editorial Team, "Mil to mm Conversion Calculator — Thou to Millimeters," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/mil-to-mm-conversion-calculator
@misc{wecalculate_mil_to_mm_conversion_calculator, title = {Mil to mm Conversion Calculator — Thou to Millimeters}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/mil-to-mm-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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