MM to Inches Converter (with Fractions)

Exact mm ↔ inches with the nearest 1/8–1/64 inch and its error, thou and a fraction chart.

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Millimetres

Inches

Type in either box. The inch box takes decimals (0.375), fractions (3/8, 1 5/16), 1-5/16 and feet and inches (7' 10 1/2").

Pick a fraction of an inch

Precision

Digit grouping

Examples

10 mm ≈ 0.3937007874 in

Rounded · in = mm ÷ 25.4 · 1 mm ≈ 0.03937007874 in

Nearest 1/64 inch: 25/64 in — 0.0031 in (0.078 mm) shorter
Thou (mil): ≈ 393.7007874 thou

Nearest fraction of an inch

The nearest mark on a rule or tape marked every 1/8, 1/16, 1/32 or 1/64 inch, and how far it is from the exact length.

Marks every	Nearest mark	Difference	Decimal inch	mm
1/8 in	3/8 in	0.0187 in (0.475 mm) shorter	0.375	9.525
1/16 in	3/8 in	0.0187 in (0.475 mm) shorter	0.375	9.525
1/32 in	13/32 in	0.0125 in (0.319 mm) longer	0.40625	10.31875
1/64 in	25/64 in	0.0031 in (0.078 mm) shorter	0.390625	9.921875

Printable fraction, mm and inch charts

Fractions → mm mm → in in → mm

Fractions of an inch to millimetres, 1/64 to 1 inch

inch	decimal inch	mm
1/64	0.015625	0.396875
1/32	0.031250	0.793750
3/64	0.046875	1.190625
1/16	0.062500	1.587500
5/64	0.078125	1.984375
3/32	0.093750	2.381250
7/64	0.109375	2.778125
1/8	0.125000	3.175000
9/64	0.140625	3.571875
5/32	0.156250	3.968750
11/64	0.171875	4.365625
3/16	0.187500	4.762500
13/64	0.203125	5.159375
7/32	0.218750	5.556250
15/64	0.234375	5.953125
1/4	0.250000	6.350000
17/64	0.265625	6.746875
9/32	0.281250	7.143750
19/64	0.296875	7.540625
5/16	0.312500	7.937500
21/64	0.328125	8.334375
11/32	0.343750	8.731250
23/64	0.359375	9.128125
3/8	0.375000	9.525000
25/64	0.390625	9.921875
13/32	0.406250	10.318750
27/64	0.421875	10.715625
7/16	0.437500	11.112500
29/64	0.453125	11.509375
15/32	0.468750	11.906250
31/64	0.484375	12.303125
1/2	0.500000	12.700000
33/64	0.515625	13.096875
17/32	0.531250	13.493750
35/64	0.546875	13.890625
9/16	0.562500	14.287500
37/64	0.578125	14.684375
19/32	0.593750	15.081250
39/64	0.609375	15.478125
5/8	0.625000	15.875000
41/64	0.640625	16.271875
21/32	0.656250	16.668750
43/64	0.671875	17.065625
11/16	0.687500	17.462500
45/64	0.703125	17.859375
23/32	0.718750	18.256250
47/64	0.734375	18.653125
3/4	0.750000	19.050000
49/64	0.765625	19.446875
25/32	0.781250	19.843750
51/64	0.796875	20.240625
13/16	0.812500	20.637500
53/64	0.828125	21.034375
27/32	0.843750	21.431250
55/64	0.859375	21.828125
7/8	0.875000	22.225000
57/64	0.890625	22.621875
29/32	0.906250	23.018750
59/64	0.921875	23.415625
15/16	0.937500	23.812500
61/64	0.953125	24.209375
31/32	0.968750	24.606250
63/64	0.984375	25.003125
1	1.000000	25.400000

All values are exact: 1/64 in = 0.015625 in = 0.396875 mm.

Millimetres to inches, 1 to 100 mm

mm	inches	nearest 1/16 in	nearest 1/64 in
1	0.0394	1/16	3/64
2	0.0787	1/16	5/64
3	0.1181	1/8	1/8
4	0.1575	3/16	5/32
5	0.1969	3/16	13/64
6	0.2362	1/4	15/64
7	0.2756	1/4	9/32
8	0.3150	5/16	5/16
9	0.3543	3/8	23/64
10	0.3937	3/8	25/64
11	0.4331	7/16	7/16
12	0.4724	1/2	15/32
13	0.5118	1/2	33/64
14	0.5512	9/16	35/64
15	0.5906	9/16	19/32
16	0.6299	5/8	5/8
17	0.6693	11/16	43/64
18	0.7087	11/16	45/64
19	0.7480	3/4	3/4
20	0.7874	13/16	25/32
21	0.8268	13/16	53/64
22	0.8661	7/8	55/64
23	0.9055	7/8	29/32
24	0.9449	15/16	15/16
25	0.9843	1	63/64
26	1.0236	1	1 1/32
27	1.0630	1 1/16	1 1/16
28	1.1024	1 1/8	1 7/64
29	1.1417	1 1/8	1 9/64
30	1.1811	1 3/16	1 3/16
31	1.2205	1 1/4	1 7/32
32	1.2598	1 1/4	1 17/64
33	1.2992	1 5/16	1 19/64
34	1.3386	1 5/16	1 11/32
35	1.3780	1 3/8	1 3/8
36	1.4173	1 7/16	1 27/64
37	1.4567	1 7/16	1 29/64
38	1.4961	1 1/2	1 1/2
39	1.5354	1 9/16	1 17/32
40	1.5748	1 9/16	1 37/64
41	1.6142	1 5/8	1 39/64
42	1.6535	1 5/8	1 21/32
43	1.6929	1 11/16	1 11/16
44	1.7323	1 3/4	1 47/64
45	1.7717	1 3/4	1 49/64
46	1.8110	1 13/16	1 13/16
47	1.8504	1 7/8	1 27/32
48	1.8898	1 7/8	1 57/64
49	1.9291	1 15/16	1 59/64
50	1.9685	1 15/16	1 31/32
51	2.0079	2	2 1/64
52	2.0472	2 1/16	2 3/64
53	2.0866	2 1/16	2 3/32
54	2.1260	2 1/8	2 1/8
55	2.1654	2 3/16	2 11/64
56	2.2047	2 3/16	2 13/64
57	2.2441	2 1/4	2 1/4
58	2.2835	2 5/16	2 9/32
59	2.3228	2 5/16	2 21/64
60	2.3622	2 3/8	2 23/64
61	2.4016	2 3/8	2 13/32
62	2.4409	2 7/16	2 7/16
63	2.4803	2 1/2	2 31/64
64	2.5197	2 1/2	2 33/64
65	2.5591	2 9/16	2 9/16
66	2.5984	2 5/8	2 19/32
67	2.6378	2 5/8	2 41/64
68	2.6772	2 11/16	2 43/64
69	2.7165	2 11/16	2 23/32
70	2.7559	2 3/4	2 3/4
71	2.7953	2 13/16	2 51/64
72	2.8346	2 13/16	2 53/64
73	2.8740	2 7/8	2 7/8
74	2.9134	2 15/16	2 29/32
75	2.9528	2 15/16	2 61/64
76	2.9921	3	2 63/64
77	3.0315	3 1/16	3 1/32
78	3.0709	3 1/16	3 5/64
79	3.1102	3 1/8	3 7/64
80	3.1496	3 1/8	3 5/32
81	3.1890	3 3/16	3 3/16
82	3.2283	3 1/4	3 15/64
83	3.2677	3 1/4	3 17/64
84	3.3071	3 5/16	3 5/16
85	3.3465	3 3/8	3 11/32
86	3.3858	3 3/8	3 25/64
87	3.4252	3 7/16	3 27/64
88	3.4646	3 7/16	3 15/32
89	3.5039	3 1/2	3 1/2
90	3.5433	3 9/16	3 35/64
91	3.5827	3 9/16	3 37/64
92	3.6220	3 5/8	3 5/8
93	3.6614	3 11/16	3 21/32
94	3.7008	3 11/16	3 45/64
95	3.7402	3 3/4	3 47/64
96	3.7795	3 3/4	3 25/32
97	3.8189	3 13/16	3 13/16
98	3.8583	3 7/8	3 55/64
99	3.8976	3 7/8	3 57/64
100	3.9370	3 15/16	3 15/16

Inches rounded to four decimal places; fractions to the nearest mark. 1 in = 25.4 mm exactly.

Inches to millimetres, 1 to 36 inches

inches	mm	cm	ft and in
1	25.4	2.54
2	50.8	5.08
3	76.2	7.62
4	101.6	10.16
5	127.0	12.70
6	152.4	15.24
7	177.8	17.78
8	203.2	20.32
9	228.6	22.86
10	254.0	25.40
11	279.4	27.94
12	304.8	30.48	1 ft 0 in
13	330.2	33.02	1 ft 1 in
14	355.6	35.56	1 ft 2 in
15	381.0	38.10	1 ft 3 in
16	406.4	40.64	1 ft 4 in
17	431.8	43.18	1 ft 5 in
18	457.2	45.72	1 ft 6 in
19	482.6	48.26	1 ft 7 in
20	508.0	50.80	1 ft 8 in
21	533.4	53.34	1 ft 9 in
22	558.8	55.88	1 ft 10 in
23	584.2	58.42	1 ft 11 in
24	609.6	60.96	2 ft 0 in
25	635.0	63.50	2 ft 1 in
26	660.4	66.04	2 ft 2 in
27	685.8	68.58	2 ft 3 in
28	711.2	71.12	2 ft 4 in
29	736.6	73.66	2 ft 5 in
30	762.0	76.20	2 ft 6 in
31	787.4	78.74	2 ft 7 in
32	812.8	81.28	2 ft 8 in
33	838.2	83.82	2 ft 9 in
34	863.6	86.36	2 ft 10 in
35	889.0	88.90	2 ft 11 in
36	914.4	91.44	3 ft 0 in

All values are exact: 1 in = 25.4 mm = 2.54 cm.

Next steps

About the MM to Inches Converter (with Fractions)

Convert millimetres to inches and inches to millimetres — type in either box and the other updates. One inch is exactly 25.4 mm, so inches = mm ÷ 25.4 and mm = inches × 25.4; 3/8 in is exactly 9.525 mm.

Every result also comes as the nearest fraction of an inch — 1/8, 1/16, 1/32 and 1/64 — with how far that mark is from the exact length, in thou (thousandths of an inch, also called mils), and in feet and inches for a foot or more. The inch box takes decimals (0.375), fractions (3/8, 1 5/16) and the hyphenated 1-5/16 of drawings and catalogues, and the fraction picker works on a phone. A printable chart lists every 64th of an inch from 1/64 to 1 inch in decimal inches and millimetres.

How to use it

Type a length in Millimetres or Inches. In the inch box, decimals (0.375), fractions (3/8, 1 5/16), 1-5/16 and feet and inches (7' 10 1/2") all work.
Or choose whole inches and a fraction under Pick a fraction of an inch.
Read the nearest 1/64 inch, thou and feet and inches under the result, and the Nearest fraction of an inch table for the 1/8, 1/16 and 1/32 inch marks with their errors.
Print the fraction chart, or switch to the mm and inch tables and copy or download them as CSV.

Examples

Millimetres to inches

Input

10 mm

Result

0.3937 in ≈ 25/64 in

10 ÷ 25.4 = 0.393701 in. 25/64 in is 9.921875 mm, 0.078 mm short of 10 mm.

A fraction to millimetres

Input

3/8 in

Result

9.525 mm (exact)

0.375 × 25.4.

A catalogue size

Input

1-5/16 in

Result

33.3375 mm

1 + 5/16 = 1.3125 in, and 1.3125 × 25.4 = 33.3375 mm.

A metric drill or bolt size

Input

6 mm

Result

0.2362 in ≈ 15/64 in

15/64 in is 5.953 mm, 0.047 mm smaller than 6 mm.

Decimal inches to a fraction

Input

0.3 in

Result

5/16 in or 19/64 in

To the nearest 1/16: 5/16 in, 0.0125 in long. To the nearest 1/64: 19/64 in, 0.0031 in short.

A drawing in millimetres

Input

2400 mm

Result

94.49 in = 7 ft 10 1/2 in

2400 ÷ 25.4 = 94.488 in = 7 ft 10.49 in.

Common uses

Matching metric bolts, drills, tubes and sheet thicknesses to inch sizes, and the other way round.
Reading an inch tape or rule against a drawing dimensioned in millimetres.
Turning decimal inches from a caliper or CAD into the nearest 1/16, 1/32 or 1/64 inch.
Printing a fraction-to-millimetre chart for a workshop wall.

The formula

NIST Handbook 44 (2026), Appendix C gives 1 inch = 2.54 cm (25.4 mm) exactly (p. C-9) and 1 mil = 0.001 inch = 0.0254 mm (p. C-11).

inches = mm ÷ 25.4 — 10 mm ÷ 25.4 = 0.3937 in
mm = inches × 25.4 — 3/8 in = 0.375 × 25.4 = 9.525 mm
thou (mil) = inches × 1,000 — 0.3937 in = 393.7 thou

Every 64th of an inch has a short exact value in millimetres (1/64 in = 0.396875 mm), so the fraction chart is exact.

Fractions of an inch and their error

Rules and tapes in inches are marked in halves, quarters, eighths and sixteenths; fine rules and fractional drill sets go down to 1/32 and 1/64 inch. To find the nearest mark, multiply the inches by the denominator and round: 0.3937 × 64 = 25.2, so the nearest 64th is 25/64 in. The converter reduces the fraction (8/16 becomes 1/2) and shows the difference: 25/64 in is 9.921875 mm, 0.078 mm (0.0031 in) shorter than 10 mm.

A metric size seldom lands exactly on a fraction, so check the difference before you swap a metric part for an inch one.

Thou, mil, and feet and inches

A thou or mil is a thousandth of an inch, 0.0254 mm; NIST Handbook 44 notes that the mil is used by some US industries to measure thickness. A mil is not a millimetre: 1 mm = 39.37 mil. For drawings dimensioned in millimetres, lengths of 12 inches or more are also shown in feet and inches, to 0.01 inch and to the nearest 1/16 inch.

Limitations

Conversions are exact; fractions are rounded to the nearest mark and the difference is shown. Halfway cases round up (1/128 in becomes 1/64 in).
Fractions finer than 1/64 inch are not offered.
For centimetres and a tape-measure drawing use the CM to Inches Converter.
Screw threads, drill numbers and wire gauges follow their own size tables; this page converts lengths only (see the Wire Gauge Converter for AWG and SWG).

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Frequently asked questions

How many inches is 1 mm?

1 mm = 1 ÷ 25.4 = 0.03937 in — about 1/25 inch, or 39.37 thou.

How many mm are in an inch?

Exactly 25.4 mm.

What is 3/8 inch in mm?

3/8 in = 0.375 in = 9.525 mm exactly.

How do I convert mm to a fraction of an inch?

Divide by 25.4 to get decimal inches, multiply by the denominator you want (16, 32 or 64) and round: 6 mm = 0.2362 in; × 64 = 15.1, so about 15/64 in.

What is a thou or a mil?

A thousandth of an inch: 1 thou = 1 mil = 0.0254 mm. It is not a millimetre.

What do “shorter” and “longer” mean?

They compare the fraction with your exact length: “25/64 in — 0.078 mm shorter” means the 25/64 inch mark falls 0.078 mm short of 10 mm.

Nearest fraction of an inch

Printable fraction, mm and inch charts

Fractions of an inch to millimetres, 1/64 to 1 inch

Millimetres to inches, 1 to 100 mm

Inches to millimetres, 1 to 36 inches

Next steps

About the MM to Inches Converter (with Fractions)

How to use it

Examples

Common uses

The formula

Fractions of an inch and their error

Thou, mil, and feet and inches

Limitations

Privacy

Frequently asked questions

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