Length
Millimetres to inches converter
One inch is exactly 25.4 mm. This converter is handy for drill bits, spanners, pipe and fixings where imperial and metric sizes meet.
Millimetres to inches converter
6 mm ≈ 0.2362 in
How to convert
inches = millimetres ÷ 25.4
millimetres = inches × 25.4
Fractional inches convert neatly: 1/8 in = 3.175 mm, 1/4 in = 6.35 mm, 3/8 in = 9.525 mm and 1/2 in = 12.7 mm, all exact.
Worked examples
- A 6 mm drill bit: 6 ÷ 25.4 ≈ 0.2362 in
- 22 mm copper pipe: 22 ÷ 25.4 ≈ 0.8661 in
- 3.175 mm, a common small tool size: 3.175 ÷ 25.4 = 0.125 in
"=" means the result is exact; "≈" means it has been rounded for display.
Millimetres to inches converter table
| Millimetres (mm) | Inches (in) |
|---|---|
| 1 | ≈ 0.0394 |
| 2 | ≈ 0.0787 |
| 3 | ≈ 0.1181 |
| 5 | ≈ 0.1969 |
| 6 | ≈ 0.2362 |
| 8 | ≈ 0.315 |
| 10 | ≈ 0.3937 |
| 12 | ≈ 0.4724 |
| 15 | ≈ 0.5906 |
| 20 | ≈ 0.7874 |
| 25 | ≈ 0.9843 |
| 25.4 | 1 |
Values marked ≈ are rounded; all others are exact.
Close, but not interchangeable
Many metric and imperial sizes look similar but are not the same. A 6 mm bit is 0.2362 in, slightly smaller than a 1/4 in bit (6.35 mm). For a loose clearance hole that may not matter, but for a tapped thread, a bearing fit or a pipe fitting it does. UK copper plumbing pipe, for example, is sold in metric sizes such as 15 mm and 22 mm, which are not the same as the older imperial 1/2 in and 3/4 in pipe, so adaptors are needed when joining old and new.
Fractions of an inch
Imperial tools are usually marked in fractions with powers of two in the denominator: halves, quarters, eighths, sixteenths, thirty-seconds and sixty-fourths. Each of these converts to an exact number of millimetres because 25.4 divided by a power of two always terminates.
Frequently asked questions
What is 1/16 inch in mm?
25.4 ÷ 16 = 1.5875 mm exactly.
Is 13 mm the same as 1/2 inch?
No. Half an inch is 12.7 mm, so 13 mm is 0.3 mm larger. A 13 mm spanner is often a loose fit on a 1/2 in nut.
How many mm in a foot?
12 × 25.4 = 304.8 mm.