Length

mil to mm conversion

Convert thousandth of an inch (mil) to millimetre (mm). Length units span pipe diameters (mm, inch), plant dimensions (m, ft), and roughness (µm) — mixing metric and imperial is routine.

1 mil = 0.0254 mm

Formula

To convert thousandth of an inch to millimetre, multiply the mil value by 0.0254. To go the other way, divide by 0.0254 (or multiply by 39.37008).

mil to mm conversion table

mil	mm
1	0.0254
2	0.0508
5	0.127
10	0.254
25	0.635
50	1.27
100	2.54
250	6.35
500	12.7
1000	25.4

Used in practice

Pipe sizes are labelled in inches (NPS) but calculated in mm; equipment layouts mix metres and feet.

Velocity scales with the inverse square of diameter, so a small length error compounds quickly in flow calculations.

Worked example. A length of 3937.008 mil is 100 mm.

Frequently asked questions

How do you convert thousandth of an inch to millimetre?

Multiply the value in mil by 0.0254 to get mm. For example, 10 mil = 0.254 mm.

What is 1 mil in mm?

1 mil equals 0.0254 mm.

Where is this conversion used?