Micron to Mil Conversion Calculator — µm ↔ thou
Convert microns (µm) to mils (thou, thousandths of an inch) and vice versa. The conversion is exact: 1 mil = 25.4 µm. Enter a value in either field to get the full conversion including millimetres, nanometres and inches.
µm
mil
1 mil = 25.4 µm exactly — derived from 1 inch = 25.4 mm
- 1
Conversion factor
1 mil = 25.4 µmExact: 1 mil = 0.001 in and 1 in = 25.4 mm, so 1 mil = 25.4 µm. - 2
Mils
254 ÷ 25.4 = 10
How does this calculator work?
mils = µm ÷ 25.4; µm = mils × 25.4. The relationship is exact (1 inch = 25.4 mm by definition). Common references: human hair ≈ 70 µm (2.76 mils), printer paper ≈ 100 µm (3.94 mils), credit card ≈ 762 µm (30 mils), standard PCB copper foil ≈ 35 µm (1.38 mils).
Formula
How this is calculated
The mil (also called thou) is a unit of length equal to one thousandth of an inch (0.001 in). Because the international inch is defined as exactly 25.4 mm, one mil equals exactly 25.4 µm — the conversion is precise with no rounding error.
Mils are widely used in the US and UK for material thicknesses: PCB copper trace widths and foil thickness, plastic film gauges, paint dry-film thickness, wire dimensions, and precision machining tolerances. Microns (µm) are the preferred SI unit for the same quantities in metric countries and in scientific literature. A standard human hair is about 70 µm (2.76 mils); a sheet of printer paper is roughly 100 µm (3.94 mils); a credit card is 762 µm (30 mils) per ISO 7810.
Note: "mil" in this context always means thousandth of an inch. "Millimetre" is abbreviated mm. In some older or informal European documentation "mil" was used to mean millimetre — if you see "mil" on a European datasheet, verify which unit is intended. This calculator uses the US/UK convention: 1 mil = 0.001 in = 25.4 µm.
Frequently asked questions
1 mil = 25.4 µm exactly, because 1 inch = 25.4 mm (exact international definition), so 1 mil = 0.001 in = 0.0254 mm = 25.4 µm. To convert mils to microns, multiply by 25.4; to convert microns to mils, divide by 25.4.
No — a mil (thou) = 0.001 inch = 25.4 µm, while a millimetre = 0.001 m = 1000 µm. They differ by a factor of 39.37. In the US packaging, plastics, and electronics industries "mil" consistently means thousandth of an inch.
Standard 1-oz PCB copper foil: 35 µm ≈ 1.38 mils. Typical plastic bag: 1.5 mil = 38.1 µm. Automotive clear coat: 40–60 µm (1.6–2.4 mils). Standard PCIe or DDR4 DIMM: gold fingers plated at 30–50 µin gold ≈ 0.76–1.27 µm. Human hair: ~70 µm ≈ 2.76 mils.
Also known as
TG we-Calculate Editorial Team. (2026). Micron to Mil Conversion Calculator — µm ↔ thou [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/micron-to-mil-conversion-calculator
TG we-Calculate Editorial Team. "Micron to Mil Conversion Calculator — µm ↔ thou." TG we-Calculate. 2026. https://we-calculate.com/calculator/micron-to-mil-conversion-calculator.
TG we-Calculate Editorial Team, "Micron to Mil Conversion Calculator — µm ↔ thou," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/micron-to-mil-conversion-calculator
@misc{wecalculate_micron_to_mil_conversion_calculator, title = {Micron to Mil Conversion Calculator — µm ↔ thou}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/micron-to-mil-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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