Micron to Mil Converter
Convert microns (µm) to mils (thou) and back, live. One mil is exactly 25.4 microns, so every result on this page is computed with exact rational math, not floating point.
µm ⇄ mil converter
All four units at once
live sync
Type in any box; the other three update instantly using the exact relations 1 mil = 0.001 in, 1 in = 25.4 mm, 1 mm = 1,000 µm.
Quick conversion tables
| Microns (µm) | Mils (thou) |
|---|
| Mils (thou) | Microns (µm) |
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Thickness in context
Paint and coating
A typical automotive paint job is 100 to 150 µm, which is 3.937008 to 5.905512 mil. Powder coating is often 60 to 80 µm, or 2.362205 to 3.149606 mil.
Typical values; always follow the product data sheet.
PCB copper weight
1 oz copper is nominally about 35 µm thick, which is 1.377953 mil. Half-ounce is about 17.5 µm (0.688976 mil); 2 oz is about 70 µm (2.755906 mil).
Nominal industry figures for 1 oz per square foot.
Plastic film
Film gauges convert exactly: 1 mil = 25.4 µm, 2 mil = 50.8 µm, 4 mil = 101.6 µm, 6 mil = 152.4 µm.
Exact by definition; no rounding involved.
Worked examples
Example 1: 100 microns to mil
Divide by the exact factor 25.4, then round half-up to 6 decimals.
Example 2: 2.5 mil to microns
Multiplying by 25.4 is exact here because 2.5 × 254 = 635, divided by 10.
Example 3: 1 mm to mil
Convert to microns first, then apply the same factor.
Example 4: 0.5 inch to mil
One inch is 1,000 mil by definition, so half an inch is 500 mil.
Related tools
Methodology
Definitions used: 1 mil (thou) = 0.001 inch exactly; 1 inch = 25.4 mm exactly (1959 international yard and pound agreement); 1 mm = 1,000 µm exactly. Therefore 1 mil = 25.4 µm exactly and 1 µm = 5/127 mil exactly.
Arithmetic: the converter uses exact rational arithmetic (BigInt fractions, e.g. ×5/127) so no binary floating-point error can enter. Displayed values are rounded half-up to your chosen decimals. Negative inputs are rejected because a thickness cannot be negative.
Frequently asked questions
What is a mil (thou)?
A mil, also called a thou, is one thousandth of an inch: 1 mil = 0.001 inch exactly. Because 1 inch is exactly 25.4 mm, one mil equals exactly 25.4 microns.
How many microns are in 1 mil?
Exactly 25.4 microns. Since 1 mil = 0.001 inch and 1 inch = 25.4 mm = 25,400 microns, multiplying gives 0.001 x 25,400 = 25.4 microns. This is an exact definition, not a rounded value.
How many mils are in 1 micron?
One micron equals 1/25.4 mil, which is approximately 0.0393700787 mil. So 100 microns = 3.937008 mil and 1,000 microns (1 mm) = 39.370079 mil.
Is a mil the same as a thou?
Yes. Mil and thou are two names for the same unit: one thousandth of an inch. Thou is short for thousandth, while mil comes from the Latin mille meaning thousand. Both equal exactly 25.4 microns.
Is a mil the same as a millimeter?
No. One mil is 0.0254 mm, so a millimeter is much larger: 1 mm = 39.370079 mil. Confusing mil with millimeter overstates a thickness by a factor of about 39.4, so always check which unit a specification uses.
Is a mil the same as a mile?
No. A mil (thou) is one thousandth of an inch, while a mile is 5,280 feet. The names look alike but the sizes differ by a factor of about 63 billion. For mile conversions, use a dedicated mile converter such as miles-to-kilometers.
What is the formula to convert microns to mil?
Divide microns by 25.4: mil = microns / 25.4. To go the other way, multiply: microns = mil x 25.4. The factor 25.4 is exact, so the only rounding is in how many decimals you choose to display.
Why is the conversion factor exactly 25.4?
Because the inch is defined as exactly 25.4 millimeters by the 1959 international yard and pound agreement, and the metric prefixes are exact by definition. Chaining 1 mil = 0.001 in, 1 in = 25.4 mm, and 1 mm = 1,000 um gives 1 mil = 25.4 um with no approximation anywhere.
How do I convert 100 microns to mil?
Divide by 25.4: 100 / 25.4 = 3.937007874... which rounds to 3.937008 mil at 6 decimals. You can check the reverse too: 3.937008 x 25.4 = 100.000003 microns, matching to the displayed precision.
What does 2 mil plastic film mean in microns?
Multiply by 25.4: 2 x 25.4 = 50.8 microns exactly. Common reference points are 1 mil = 25.4 um, 4 mil = 101.6 um, and 6 mil = 152.4 um. Plastic film is usually specified in mil in the US and in microns elsewhere.
Are paint thicknesses given in mil or microns?
Both, depending on the industry. A typical automotive paint job is 100 to 150 microns, which is 3.937008 to 5.905512 mil. Powder coating is often 60 to 80 microns, or 2.362205 to 3.149606 mil. US coating specs lean toward mil; European specs lean toward microns.
How thick is 1 oz PCB copper in mil and microns?
One ounce copper (1 oz per square foot) is nominally about 35 microns thick, which converts to 1.377953 mil. Half-ounce copper is about 17.5 microns (0.688976 mil) and 2 oz copper is about 70 microns (2.755906 mil).
How is this different from a mesh-to-micron converter?
A micron-to-mil converter translates a plain length between two units using the exact factor 25.4. A mesh-to-micron converter instead maps a sieve mesh number (openings per inch, ASTM E11) to an approximate opening size in microns, which depends on wire diameter and the standard's table. They answer different questions.
How precise are the results on this page?
The math is exact rational arithmetic: microns to mil multiplies by 5/127, the exact fraction behind 1/25.4, with no floating-point error. Displayed values are rounded half-up to the decimals you select (default 6), and the show-your-work panel shows the unrounded fraction.
Can I convert millimeters or inches here too?
Yes. The multi-unit panel converts between microns, millimeters, mil (thou), and inches live: type in any one box and the other three update. For longer lengths, a general length-converter is the better tool.
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