Millimeters to Inches

Convert millimetres to inches in decimal and nearest sixteenth fractions for machining and workshop use, in your browser. Runs entirely in your browser — your numbers never leave this device.

Value in millimetres

Millimetres → Inches

1 in

25.4 mm = 1 in — also 1 in

Millimetres to inches — 1 to 100 mm

Millimetres	Inches
1 mm	0.03937 in
2 mm	0.07874 in
3 mm	0.11811 in
4 mm	0.15748 in
5 mm	0.19685 in
6 mm	0.23622 in
7 mm	0.275591 in
8 mm	0.314961 in
9 mm	0.354331 in
10 mm	0.393701 in
11 mm	0.433071 in
12 mm	0.472441 in
13 mm	0.511811 in
14 mm	0.551181 in
15 mm	0.590551 in
16 mm	0.629921 in
17 mm	0.669291 in
18 mm	0.708661 in
19 mm	0.748031 in
20 mm	0.787402 in
21 mm	0.826772 in
22 mm	0.866142 in
23 mm	0.905512 in
24 mm	0.944882 in
25 mm	0.984252 in
26 mm	1.023622 in
27 mm	1.062992 in
28 mm	1.102362 in
29 mm	1.141732 in
30 mm	1.181102 in
31 mm	1.220472 in
32 mm	1.259843 in
33 mm	1.299213 in
34 mm	1.338583 in
35 mm	1.377953 in
36 mm	1.417323 in
37 mm	1.456693 in
38 mm	1.496063 in
39 mm	1.535433 in
40 mm	1.574803 in
41 mm	1.614173 in
42 mm	1.653543 in
43 mm	1.692913 in
44 mm	1.732283 in
45 mm	1.771654 in
46 mm	1.811024 in
47 mm	1.850394 in
48 mm	1.889764 in
49 mm	1.929134 in
50 mm	1.968504 in
51 mm	2.007874 in
52 mm	2.047244 in
53 mm	2.086614 in
54 mm	2.125984 in
55 mm	2.165354 in
56 mm	2.204724 in
57 mm	2.244094 in
58 mm	2.283465 in
59 mm	2.322835 in
60 mm	2.362205 in
61 mm	2.401575 in
62 mm	2.440945 in
63 mm	2.480315 in
64 mm	2.519685 in
65 mm	2.559055 in
66 mm	2.598425 in
67 mm	2.637795 in
68 mm	2.677165 in
69 mm	2.716535 in
70 mm	2.755906 in
71 mm	2.795276 in
72 mm	2.834646 in
73 mm	2.874016 in
74 mm	2.913386 in
75 mm	2.952756 in
76 mm	2.992126 in
77 mm	3.031496 in
78 mm	3.070866 in
79 mm	3.110236 in
80 mm	3.149606 in
81 mm	3.188976 in
82 mm	3.228346 in
83 mm	3.267717 in
84 mm	3.307087 in
85 mm	3.346457 in
86 mm	3.385827 in
87 mm	3.425197 in
88 mm	3.464567 in
89 mm	3.503937 in
90 mm	3.543307 in
91 mm	3.582677 in
92 mm	3.622047 in
93 mm	3.661417 in
94 mm	3.700787 in
95 mm	3.740157 in
96 mm	3.779528 in
97 mm	3.818898 in
98 mm	3.858268 in
99 mm	3.897638 in
100 mm	3.937008 in

Batch convert — one value per line

How it works

Inches = millimetres ÷ 25.4 (because 1 inch = 25.4 mm exactly); nearest sixteenth = round(inches × 16) ÷ 16

Millimetres to inches: decimal and nearest sixteenth of an inch

Millimetres	Inches (decimal)	Nearest 1/16 in
1 mm	0.0394	1/16
2 mm	0.0787	1/16
3 mm	0.1181	1/8
5 mm	0.1969	3/16
6 mm	0.2362	1/4
10 mm	0.3937	3/8
12 mm	0.4724	1/2
15 mm	0.5906	9/16
20 mm	0.7874	13/16
25 mm	0.9843	1

Millimetres convert to inches by dividing by 25.4, the exact definition of the inch in millimetres: 10 mm is 10 ÷ 25.4 = 0.3937 inches. Machining and workshop work then faces a second step that a bare decimal does not solve — expressing that decimal as the fraction a caliper dial, drill chart or imperial drawing uses, in halves, quarters, eighths or sixteenths of an inch.

This page shows both forms. The nearest sixteenth is found by multiplying the decimal inches by 16 and rounding: 6 mm is 0.2362 inches, and 0.2362 × 16 = 3.78, which rounds to 4 sixteenths — a quarter inch. Some sizes land almost exactly (25 mm = 0.9843 in, effectively 1 inch at 16/16; 12 mm = 0.4724 in, close to 1/2 inch at 8/16), while others sit distinctly between fractions, which the decimal figure makes visible.

Choose the form by tolerance. A fraction is right for choosing a drill or checking a bolt against a chart; a decimal to three or four places is right for machining dimensions, where a sixteenth (about 1.59 mm) is far too coarse a step. Batch mode converts a pasted list of millimetre sizes with the same division.

Worked examples

A bolt diameter

Input: 8 mm to inches and nearest sixteenth.
Working: 8 ÷ 25.4 = 0.31496 inches. Sixteenths: 0.31496 × 16 = 5.04, which rounds to 5, so 5/16.
Result: 8 mm = 0.3150 in, about 5/16 in

A drill size

Input: 6 mm to inches.
Working: 6 ÷ 25.4 = 0.23622. Sixteenths: 0.23622 × 16 = 3.78, rounding to 4, so 1/4.
Result: 6 mm = 0.2362 in, about 1/4 in

A larger component

Input: 100 mm to inches.
Working: 100 ÷ 25.4 = 3.93701.
Result: 100 mm = 3.9370 in

Frequently asked questions

How many millimetres are in an inch?

Exactly 25.4, by definition. So millimetres to inches divides by 25.4, and inches to millimetres multiplies by 25.4. A half inch is therefore exactly 12.7 mm, which is why 12 mm (0.4724 in) is close to but not exactly a half inch.

How do I find the nearest fraction for a millimetre size?

Convert to decimal inches, multiply by 16 and round to the nearest whole number — that is the count of sixteenths. For 19 mm: 19 ÷ 25.4 = 0.7480 in, and 0.7480 × 16 = 11.97, which rounds to 12 sixteenths, or 3/4 inch. Simplify the sixteenths (4/16 = 1/4, 8/16 = 1/2) for the form charts use.

Is 10 mm the same as 3/8 of an inch?

Close, but not exact. 3/8 inch is 0.375 × 25.4 = 9.525 mm, while 10 mm is 0.3937 inches. The gap is about 0.48 mm — small enough for a clearance hole in many cases, large enough to matter for a press fit or a threaded part. The decimal column in the table keeps that distinction visible.

Why do some tables give 25 mm as exactly 1 inch?

They are rounding to the nearest sixteenth, where 25 mm (0.9843 in) does land on 16/16. As an exact statement it is wrong by 0.4 mm, since 1 inch is 25.4 mm. This page shows the exact decimal alongside the fraction so the approximation is never mistaken for the definition.

Can I convert a list of drill or bolt sizes at once?

Yes. Batch mode divides every pasted line by 25.4, so a metric drill set list or a column of component sizes converts together, with the fraction view available for chart matching. That is the task a single-answer widget makes tedious.