A mil (or thou) is one thousandth of an inch, 25.4 µm. Plastic sheeting, garbage bags, paint films and circuit-board traces are specified in mils in North America. It is not the same as a millimetre.
How to use the Mil
- Pick the unit you are starting from in the From menu and type your value.
- Pick the unit you want in the To menu. The heading changes to match – for example “Mils to Inches Converter”.
- The most common length units are shown below at the same time, so you can compare them at a glance.
- Type into any result to convert backwards, then use Copy results – the copied text starts with the heading for your chosen units.
Results update as you type. Everything is calculated in your browser.
How it works
Every length unit is defined by an exact factor relative to the metre (the base unit). The calculator first turns the value you type into metres, then turns that into the unit you picked in the “To” menu and into each of the common units below it. This two-step method means any unit can be converted to any other – 27 units are available in each menu – and you can type into any field, including a result, to work in the other direction. Changing a unit menu keeps the quantity the same and just re-expresses it, and the page heading and copied results follow your choice.
How to convert length units
- Choose the unit you have in the From menu and type the value, for example 1 mil.
- Choose the unit you want in the To menu, for example inches. The page heading changes to “Mils to Inches Converter”.
- The calculator multiplies by the metre factor of the “from” unit and divides by the factor of the “to” unit: 1 mil × 2.54 × 10-5 ÷ 0.0254 = 0.001 in.
1 mil (thou) in common units
| Unit | Value |
|---|---|
| Inches (in) | 0.001 |
| Millimetres (mm) | 0.0254 |
| Micrometres (µm) | 25.4 |
| Centimetres (cm) | 0.00254 |
Mils conversion table
| Mils | in | mm | µm | cm |
|---|---|---|---|---|
| 1 | 0.001 | 0.0254 | 25.4 | 0.00254 |
| 2 | 0.002 | 0.0508 | 50.8 | 0.00508 |
| 4 | 0.004 | 0.1016 | 101.6 | 0.01016 |
| 6 | 0.006 | 0.1524 | 152.4 | 0.01524 |
| 10 | 0.01 | 0.254 | 254 | 0.0254 |
| 20 | 0.02 | 0.508 | 508 | 0.0508 |
| 40 | 0.04 | 1.016 | 1,016 | 0.1016 |
What is a mil?
A mil (or thou) is one thousandth of an inch, 25.4 µm. It is used in North America for plastic film, garbage bags, paint and coating thickness and circuit-board traces; it is not a millimetre.
What is an inch?
The inch has been defined as exactly 25.4 mm since 1959. It is used in the U.S. for almost everything and worldwide for screen sizes, wheel and tyre sizes, pipe threads and many tools.
What is a millimetre?
A millimetre is one thousandth of a metre. Engineering drawings, construction plans, rainfall, screws, bolts and jewellery are all dimensioned in millimetres.
Common mistakes to avoid
Mixing the international foot (0.3048 m) with the old u.s. survey foot, confusing nautical and statute miles, and writing decimal feet such as 5.5 ft as “5 ft 5 in” (it is 5 ft 6 in).
Formula
1 mil = 0.001 in1 mil = 0.0254 mm1 mil = 25.4 µm1 mil = 0.00254 cmWorked example
Inputs — From: 1 mil.
Results — To = 0.001 in; Millimetres = 0.0254 mm; Micrometres = 25.4 µm; Centimetres = 0.00254 cm.
Frequently asked questions
Is a mil a millimetre?
No. 1 mil = 0.0254 mm; 1 mm is about 39.37 mil.
How thick is 6 mil plastic?
About 0.15 mm.
How many mils in an inch?
1,000.
How do I change the units?
Pick any unit in the From and To menus. The value is converted in place, and the heading changes to show your conversion, for example “Mils to Inches Converter”.
Can I type into any field?
Yes. Every field is editable, so you can start from whichever unit you have.
How many units can I convert between?
27 length units, from the everyday to the specialised.
Which units are exact?
All factors here are exact by definition except astronomical and similar reference values, which use internationally agreed constants.
What formula does the Mil use?
1 mil = 0.001 in.