Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Convert millimeters to mils (thousandths of an inch) and back.
A "mil" (also called a "thou") is one thousandth of an inch -- a small unit used almost exclusively for specifying the thickness of thin materials like plastic sheeting, laminate film, wire coatings, and coating layers. Manufacturing specs, packaging films, and PCB (printed circuit board) trace widths often list thickness in mils, while measurements elsewhere are usually in millimeters -- this converter translates between the two exactly.
Enter your measurement and choose whether it's currently in Millimeters or Mils from the "From Unit" dropdown. Both results update instantly as you type.
Mils = Millimeters × 39.37007874015748
Millimeters = Mils × 0.0254
A mil is exactly 0.0254mm (one thousandth of the exact 25.4mm-per-inch definition), so this conversion is precise, not approximated. 39.37007874015748 is the exact reciprocal (1 ÷ 0.0254).
| Millimeters | Mils |
|---|---|
| 0.025 | 0.98 |
| 0.05 | 1.97 |
| 0.1 | 3.94 |
| 0.5 | 19.69 |
| 1 | 39.37 |
| 2.5 | 98.43 |
Manufacturers and buyers use this to check plastic film, sheeting, or coating thickness specs against a metric measurement. Electronics engineers use it when a PCB trace width or copper layer thickness is given in mils but the rest of a design uses millimeters.
Don't confuse "mil" (thousandth of an inch, used for thickness) with "mile" -- they're unrelated units that are sometimes mixed up due to the similar abbreviation. Also note that in some countries, "mil" can refer to a different unit (like the Swedish/Norwegian "mil" meaning 10km) -- this converter uses the US/imperial thousandth-of-an-inch definition throughout.
Mils are used for very thin materials, where a difference of a few thousandths of an inch can change how a product behaves. A film that is 3 mils thick is noticeably more flexible than one at 6 mils, and a coating that is too thin or too thick can fail to protect or fit. Because of this, it is worth entering your measurement carefully and keeping enough decimal places, rather than rounding early.
To turn a result into inches, divide mils by 1,000. So 11.81 mils is about 0.0118 inch. That extra step is handy when a datasheet lists inches but a drawing lists millimeters.
Getting a trustworthy input is often harder than the conversion. A micrometer or digital caliper is the usual tool for thin sheet. A ruler is not precise enough for materials below a millimeter or so. When measuring film or paper, avoid squeezing the jaws hard, since soft materials compress and read thinner than they really are. Take a few readings at different spots and average them, because thickness can vary across a sheet. If you are checking a purchase against a specification, compare the tolerance given by the manufacturer, since a nominal thickness usually allows some variation.
A buyer working from a metric datasheet and a supplier quoting in mils may each be correct, yet talk past each other. Convert both to the same unit before comparing prices or performance. Also note that the word gauge is sometimes used for film thickness with a different meaning, so if a document says gauge rather than mils, verify the definition with the supplier before converting.
One thousandth of an inch (0.001in), also called a "thou" -- commonly used for specifying the thickness of thin materials like plastic film, coatings, and wire insulation.
No -- they're easily confused by name but very different sizes. 1 millimeter equals about 39.37 mils, so a millimeter is a much larger unit.
6 mils equals 0.1524mm -- a common thickness for heavy-duty trash bags and painter's plastic sheeting.
Divide by 1,000. For example, 25 mils is 0.025 inch.
A micrometer or a good digital caliper. A ruler lacks the precision required, and pressing too hard can compress soft films and give a low reading.
Not necessarily. Gauge has different meanings for different materials and industries, so confirm the definition before converting.
The exact millimeters-to-mils factor is 39.37008 -- multiply to convert forward, or multiply by 0.0254 to convert mils back to millimeters. For example, 12.5 millimeters × 39.37008 = 492.126 mils, and 25 millimeters × 39.37008 = 984.252 mils.
One millimeter equals exactly 0.001 meters, or about 0.0393701 inches. One mil (a thousandth of an inch) equals exactly 0.0254 millimeters.
| Millimeters | Mils |
|---|---|
| 1 | 39.37008 |
| 2 | 78.74016 |
| 3 | 118.1102 |
| 5 | 196.8504 |
| 10 | 393.7008 |
| 15 | 590.5512 |
| 20 | 787.4016 |
| 25 | 984.252 |
| 50 | 1,968.504 |
| 75 | 2,952.756 |
| 100 | 3,937.008 |
| 250 | 9,842.52 |
| 500 | 19,685.04 |
| 1,000 | 39,370.08 |
How many mils are in 1 millimeters?
1 millimeters equals 39.37008 mils.
How many millimeters are in 1 mils?
1 mils equals 0.0254 millimeters.
What is 3.5 millimeters in mils?
3.5 millimeters equals 137.7953 mils, using the same 39.37008 factor as the rest of this chart.
Is this conversion exact or approximate?
The 39.37008 factor comes from a fixed, exact definitional constant, so the underlying math is exact; the numbers on this page are rounded to seven significant digits for readability, and the calculator above keeps the full-precision value.
Values are rounded to seven significant digits for display; the converter above uses the full-precision factor.
Reference: NIST Weights and Measures