Inches Mm Conversion

Reference data and engineering information about inches mm conversion for basics applications.

inchesconversionCalculator

Overview

Inch-to-millimeter conversion is one of the most frequent calculations in engineering, manufacturing, and construction. The inch is the standard unit in the US customary and imperial systems, while the millimeter dominates metric-based design worldwide. One inch is exactly 25.4 mm by international agreement (since 1959).

This page provides conversion formulas, quick-reference tables for fractional and decimal inches, and interactive calculators for fast field use.

Key Formulas

How many millimeters in an inch?

There are exactly 25.4 millimeters in one inch.

Inches to millimeters:

$mm = inches \times 25.4$

Millimeters to inches:

$inches = mm \div 25.4$

Both relationships are exact — no rounding factor is involved.

Variables

Symbol	Description	Unit
$in$	Length in inches	in
$mm$	Length in millimeters	mm

Quick Converters

Convert in either direction. The constants used are exact.

Inches to Millimeters

Inches(in)

Millimeters to Inches

Millimeters(mm)

Fractional Inches to Millimeters

Common fractional inch sizes used in machining, fasteners, and drill sets, with their decimal and metric equivalents.

16 rows

Fractional Inches to Decimal Inches and Metric Millimeters
Fractional Inches	Decimal Inches	Millimeters(mm)
1/64	0.0156	0.3969
1/32	0.0313	0.7938
1/16	0.0625	1.5875
1/8	0.125	3.175
3/16	0.1875	4.7625
1/4	0.25	6.35
5/16	0.3125	7.9375
3/8	0.375	9.525
7/16	0.4375	11.1125
1/2	0.5	12.7
9/16	0.5625	14.2875
5/8	0.625	15.875
11/16	0.6875	17.4625
3/4	0.75	19.05
7/8	0.875	22.225
1	1	25.4

Source: engineeringtoolbox.com

Decimal Inches to Millimeters

Useful for decimal readings from calipers and CAD dimensioning.

16 rows

Decimal Inches to Millimeters
Inches(in)	Millimeters(mm)
0.1	2.54
0.2	5.08
0.3	7.62
0.4	10.16
0.5	12.7
0.6	15.24
0.7	17.78
0.8	20.32
0.9	22.86
1	25.4
2	50.8
5	127
10	254
12	304.8
24	609.6
36	914.4

Source: engineeringtoolbox.com

Millimeters to Inches

mm to Inches Chart

14 rows

Millimeters to Inches
Millimeters(mm)	Inches(in)
1	0.0394
2	0.0787
5	0.1969
10	0.3937
20	0.7874
25	0.9843
50	1.9685
75	2.9528
100	3.937
150	5.9055
200	7.874
300	11.811
500	19.685
1000	39.3701

Source: engineeringtoolbox.com

Inch-Millimeter Relationship

The chart below shows the exact linear relationship between inches and millimeters. Because the conversion factor is constant, the plot is a straight line through the origin.

Inches vs Millimeters

Restored Original Source Tables

The following tables are restored from the original source page to preserve the complete reference data.

Inches to mm Conversion table in pdf format.

Download and print inches to mm chart.

Convert between fractional and/or decimal inches and metric millimeters

246 rows

Convert between fractional and/or decimal inches and metric millimeters
Fractional	Decimal	mm
.	0.0039	0.1
.	0.0079	0.2
.	0.0118	0.3
1/64	0.0156	0.3969
.	0.0157	0.4
.	0.0197	0.5
.	0.0236	0.6
.	0.0276	0.7
1/32	0.0313	0.7938
.	0.0315	0.8
.	0.0354	0.9
.	0.0394	1
.	0.0433	1.1
3/64	0.0469	1.1906
.	0.0472	1.2
.	0.0512	1.3
.	0.0551	1.4
.	0.0591	1.5
1/16	0.0625	1.5875
.	0.063	1.6
.	0.0669	1.7
.	0.0709	1.8
.	0.0748	1.9
5/64	0.0781	1.9844
.	0.0787	2
.	0.0827	2.1
.	0.0866	2.2
.	0.0906	2.3
3/32	0.0938	2.3813
.	0.0945	2.4
.	0.0984	2.5
7/64	0.1094	2.7781
.	0.1181	3
1/8	0.125	3.175
.	0.1378	3.5
9/64	0.1406	3.5719
5/32	0.1563	3.9688
.	0.1575	4
11/64	0.1719	4.3656
.	0.1772	4.5
3/16	0.1875	4.7625
.	0.1969	5
13/64	0.2031	5.1594
.	0.2165	5.5
7/32	0.2188	5.5563
15/64	0.2344	5.9531
.	0.2362	6
1/4	0.25	6.35
.	0.2559	6.5
17/64	0.2656	6.7469
.	0.2756	7
9/32	0.2813	7.1438
.	0.2953	7.5
19/64	0.2969	7.5406
5/16	0.3125	7.9375
.	0.315	8
21/64	0.3281	8.3344
.	0.3346	8.5
11/32	0.3438	8.7313
.	0.3543	9
23/64	0.3594	9.1281
.	0.374	9.5
3/8	0.375	9.525
25/64	0.3906	9.9219
.	0.3937	10
13/32	0.4063	10.3188
.	0.4134	10.5
27/64	0.4219	10.7156
.	0.4331	11
7/16	0.4375	11.1125
.	0.4528	11.5
29/64	0.4531	11.5094
15/32	0.4688	11.9063
.	0.4724	12
31/64	0.4844	12.3031
.	0.4921	12.5
1/2	0.5	12.7
.	0.5118	13
33/64	0.5156	13.0969
17/32	0.5313	13.4938
.	0.5315	13.5
35/64	0.5469	13.8906
.	0.5512	14
9/16	0.5625	14.2875
.	0.5709	14.5
37/64	0.5781	14.6844
.	0.5906	15
19/32	0.5938	15.0813
39/64	0.6094	15.4781
.	0.6102	15.5
5/8	0.625	15.875
.	0.6299	16
41/64	0.6406	16.2719
.	0.6496	16.5
21/32	0.6563	16.6688
.	0.6693	17
43/64	0.6719	17.0656
11/16	0.6875	17.4625
.	0.689	17.5
45/64	0.7031	17.8594
.	0.7087	18
23/32	0.7188	18.2563
.	0.7283	18.5
47/64	0.7344	18.6531
.	0.748	19
3/4	0.75	19.05
49/64	0.7656	19.4469
.	0.7677	19.5
25/32	0.7813	19.8438
.	0.7874	20
51/64	0.7969	20.2406
.	0.8071	20.5
13/16	0.8125	20.6375
.	0.8268	21
53/64	0.8281	21.0344
27/32	0.8438	21.4313
.	0.8465	21.5
55/64	0.8594	21.8281
.	0.8661	22
7/8	0.875	22.225
.	0.8858	22.5
57/64	0.89063	22.6219
.	0.9055	23
29/32	0.90625	23.0188
59/64	0.92188	23.4156
.	0.9252	23.5
15/16	0.9375	23.8125
.	0.9449	24
61/64	0.95313	24.2094
.	0.9646	24.5
31/32	0.96875	24.6063
.	0.9843	25
63/64	0.98438	25.0031
1	1	25.4
.	1.0039	25.5
.	1.0236	26
.	1.0433	26.5
.	1.063	27
.	1.0827	27.5
.	1.1024	28
.	1.122	28.5
.	1.1417	29
.	1.1614	29.5
.	1.1811	30
.	1.2205	31
1 1/4	1.25	31.75
.	1.2598	32
.	1.2992	33
.	1.3386	34
.	1.378	35
.	1.4173	36
.	1.4567	37
.	1.4961	38
1 1/2	1.5	38.1
.	1.5354	39
.	1.5748	40
.	1.6142	41
.	1.6535	42
.	1.6929	43
.	1.7323	44
1 3/4	1.75	44.45
.	1.7717	45
.	1.811	46
.	1.8504	47
.	1.8898	48
.	1.9291	49
.	1.9685	50
2	2	50.8
.	2.0079	51
.	2.0472	52
.	2.0866	53
.	2.126	54
.	2.1654	55
.	2.2047	56
.	2.2441	57
2 1/4	2.25	57.15
.	2.2835	58
.	2.3228	59
.	2.3622	60
.	2.4016	61
.	2.4409	62
.	2.4803	63
2 1/2	2.5	63.5
.	2.5197	64
.	2.5591	65
.	2.5984	66
.	2.6378	67
.	2.6772	68
.	2.7165	69
2 3/4	2.75	69.85
.	2.7559	70
.	2.7953	71
.	2.8346	72
.	2.874	73
.	2.9134	74
.	2.9528	75
.	2.9921	76
3	3	76.2
.	3.0315	77
.	3.0709	78
.	3.1102	79
.	3.1496	80
.	3.189	81
.	3.2283	82
.	3.2677	83
.	3.3071	84
.	3.3465	85
.	3.3858	86
.	3.4252	87
.	3.4646	88
3 1/2	3.5	88.9
.	3.5039	89
.	3.5433	90
.	3.5827	91
.	3.622	92
.	3.6614	93
.	3.7008	94
.	3.7402	95
.	3.7795	96
.	3.8189	97
.	3.8583	98
.	3.8976	99
.	3.937	100
4	4	101.6
.	4.3307	110
4 1/2	4.5	114.3
.	4.7244	120
5	5	127
.	5.1181	130
.	5.5118	140
.	5.9055	150
6	6	152.4
.	6.2992	160
.	6.6929	170
.	7.0866	180
.	7.4803	190
.	7.874	200
8	8	203.2
.	9.8425	250
10	10	254
20	20	508
30	30	762
40	40	1016
60	60	1524
80	80	2032
100	100	2540

Source: engineeringtoolbox.com

Convert from decimal inches to mm

11 rows

Convert from decimal inches to mm
inches	mm	mm	mm	mm	mm	mm	mm	mm	mm	mm
0	0.01	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.09
0	0	0.25	0.51	0.76	1.02	1.27	1.52	1.78	2.03	2.29
0.1	2.54	2.79	3.05	3.3	3.56	3.81	4.06	4.32	4.57	4.83
0.2	5.08	5.33	5.59	5.84	6.1	6.35	6.6	6.86	7.11	7.37
0.3	7.62	7.87	8.13	8.38	8.64	8.89	9.14	9.4	9.65	9.91
0.4	10.16	10.41	10.67	10.92	11.18	11.43	11.68	11.94	12.19	12.45
0.5	12.7	12.95	13.21	13.46	13.72	13.97	14.22	14.48	14.73	14.99
0.6	15.24	15.49	15.75	16	16.26	16.51	16.76	17.02	17.27	17.53
0.7	17.78	18.03	18.29	18.54	18.8	19.05	19.3	19.56	19.81	20.07
0.8	20.32	20.57	20.83	21.08	21.34	21.59	21.84	22.1	22.35	22.61
0.9

Source: engineeringtoolbox.com

Convert from mm to decimal inches

102 rows

Convert from mm to decimal inches
mm	inches	inches	inches	inches	inches	inches	inches	inches	inches	inches
0	1	2	3	4	5	6	7	8	9
0	0	0.0394	0.0787	0.118	0.157	0.197	0.236	0.276	0.315	0.354
10	0.394	0.433	0.472	0.512	0.551	0.591	0.63	0.669	0.709	0.748
20	0.787	0.827	0.866	0.906	0.945	0.984	1.02	1.06	1.1	1.14
30	1.18	1.22	1.26	1.3	1.34	1.38	1.42	1.46	1.5	1.54
40	1.57	1.61	1.65	1.69	1.73	1.77	1.81	1.85	1.89	1.93
50	1.97	2.01	2.05	2.09	2.13	2.17	2.2	2.24	2.28	2.32
60	2.36	2.4	2.44	2.48	2.52	2.56	2.6	2.64	2.68	2.72
70	2.76	2.8	2.83	2.87	2.91	2.95	2.99	3.03	3.07	3.11
80	3.15	3.19	3.23	3.27	3.31	3.35	3.39	3.43	3.46	3.5
90	3.54	3.58	3.62	3.66	3.7	3.74	3.78	3.82	3.86	3.9
100	3.94	3.98	4.02	4.06	4.09	4.13	4.17	4.21	4.25	4.29
110	4.33	4.37	4.41	4.45	4.49	4.53	4.57	4.61	4.65	4.69
120	4.72	4.76	4.8	4.84	4.88	4.92	4.96	5	5.04	5.08
130	5.12	5.16	5.2	5.24	5.28	5.31	5.35	5.39	5.43	5.47
140	5.51	5.55	5.59	5.63	5.67	5.71	5.75	5.79	5.83	5.87
150	5.91	5.94	5.98	6.02	6.06	6.1	6.14	6.18	6.22	6.26
160	6.3	6.34	6.38	6.42	6.46	6.5	6.54	6.57	6.61	6.65
170	6.69	6.73	6.77	6.81	6.85	6.89	6.93	6.97	7.01	7.05
180	7.09	7.13	7.17	7.2	7.24	7.28	7.32	7.36	7.4	7.44
190	7.48	7.52	7.56	7.6	7.64	7.68	7.72	7.76	7.8	7.83
200	7.87	7.91	7.95	7.99	8.03	8.07	8.11	8.15	8.19	8.23
210	8.27	8.31	8.35	8.39	8.43	8.46	8.5	8.54	8.58	8.62
220	8.66	8.7	8.74	8.78	8.82	8.86	8.9	8.94	8.98	9.02
230	9.06	9.09	9.13	9.17	9.21	9.25	9.29	9.33	9.37	9.41
240	9.45	9.49	9.53	9.57	9.61	9.65	9.69	9.72	9.76	9.8
250	9.84	9.88	9.92	9.96	10	10	10.1	10.1	10.2	10.2
260	10.2	10.3	10.3	10.4	10.4	10.4	10.5	10.5	10.6	10.6
270	10.6	10.7	10.7	10.7	10.8	10.8	10.9	10.9	10.9	11
280	11	11.1	11.1	11.1	11.2	11.2	11.3	11.3	11.3	11.4
290	11.4	11.5	11.5	11.5	11.6	11.6	11.7	11.7	11.7	11.8
300	11.8	11.9	11.9	11.9	12	12	12	12.1	12.1	12.2
310	12.2	12.2	12.3	12.3	12.4	12.4	12.4	12.5	12.5	12.6
320	12.6	12.6	12.7	12.7	12.8	12.8	12.8	12.9	12.9	13
330	13	13	13.1	13.1	13.1	13.2	13.2	13.3	13.3	13.3
340	13.4	13.4	13.5	13.5	13.5	13.6	13.6	13.7	13.7	13.7
350	13.8	13.8	13.9	13.9	13.9	14	14	14.1	14.1	14.1
360	14.2	14.2	14.3	14.3	14.3	14.4	14.4	14.4	14.5	14.5
370	14.6	14.6	14.6	14.7	14.7	14.8	14.8	14.8	14.9	14.9
380	15	15	15	15.1	15.1	15.2	15.2	15.2	15.3	15.3
390	15.4	15.4	15.4	15.5	15.5	15.6	15.6	15.6	15.7	15.7
400	15.7	15.8	15.8	15.9	15.9	15.9	16	16	16.1	16.1
410	16.1	16.2	16.2	16.3	16.3	16.3	16.4	16.4	16.5	16.5
420	16.5	16.6	16.6	16.7	16.7	16.7	16.8	16.8	16.9	16.9
430	16.9	17	17	17	17.1	17.1	17.2	17.2	17.2	17.3
440	17.3	17.4	17.4	17.4	17.5	17.5	17.6	17.6	17.6	17.7
450	17.7	17.8	17.8	17.8	17.9	17.9	18	18	18	18.1
460	18.1	18.1	18.2	18.2	18.3	18.3	18.3	18.4	18.4	18.5
470	18.5	18.5	18.6	18.6	18.7	18.7	18.7	18.8	18.8	18.9
480	18.9	18.9	19	19	19.1	19.1	19.1	19.2	19.2	19.3
490	19.3	19.3	19.4	19.4	19.4	19.5	19.5	19.6	19.6	19.6
500	19.7	19.7	19.8	19.8	19.8	19.9	19.9	20	20	20
510	20.1	20.1	20.2	20.2	20.2	20.3	20.3	20.4	20.4	20.4
520	20.5	20.5	20.6	20.6	20.6	20.7	20.7	20.7	20.8	20.8
530	20.9	20.9	20.9	21	21	21.1	21.1	21.1	21.2	21.2
540	21.3	21.3	21.3	21.4	21.4	21.5	21.5	21.5	21.6	21.6
550	21.7	21.7	21.7	21.8	21.8	21.9	21.9	21.9	22	22
560	22	22.1	22.1	22.2	22.2	22.2	22.3	22.3	22.4	22.4
570	22.4	22.5	22.5	22.6	22.6	22.6	22.7	22.7	22.8	22.8
580	22.8	22.9	22.9	23	23	23	23.1	23.1	23.1	23.2
590	23.2	23.3	23.3	23.3	23.4	23.4	23.5	23.5	23.5	23.6
600	23.6	23.7	23.7	23.7	23.8	23.8	23.9	23.9	23.9	24
610	24	24.1	24.1	24.1	24.2	24.2	24.3	24.3	24.3	24.4
620	24.4	24.4	24.5	24.5	24.6	24.6	24.6	24.7	24.7	24.8
630	24.8	24.8	24.9	24.9	25	25	25	25.1	25.1	25.2
640	25.2	25.2	25.3	25.3	25.4	25.4	25.4	25.5	25.5	25.6
650	25.6	25.6	25.7	25.7	25.7	25.8	25.8	25.9	25.9	25.9
660	26	26	26.1	26.1	26.1	26.2	26.2	26.3	26.3	26.3
670	26.4	26.4	26.5	26.5	26.5	26.6	26.6	26.7	26.7	26.7
680	26.8	26.8	26.9	26.9	26.9	27	27	27	27.1	27.1
690	27.2	27.2	27.2	27.3	27.3	27.4	27.4	27.4	27.5	27.5
700	27.6	27.6	27.6	27.7	27.7	27.8	27.8	27.8	27.9	27.9
710	28	28	28	28.1	28.1	28.1	28.2	28.2	28.3	28.3
720	28.3	28.4	28.4	28.5	28.5	28.5	28.6	28.6	28.7	28.7
730	28.7	28.8	28.8	28.9	28.9	28.9	29	29	29.1	29.1
740	29.1	29.2	29.2	29.3	29.3	29.3	29.4	29.4	29.4	29.5
750	29.5	29.6	29.6	29.6	29.7	29.7	29.8	29.8	29.8	29.9
760	29.9	30	30	30	30.1	30.1	30.2	30.2	30.2	30.3
770	30.3	30.4	30.4	30.4	30.5	30.5	30.6	30.6	30.6	30.7
780	30.7	30.7	30.8	30.8	30.9	30.9	30.9	31	31	31.1
790	31.1	31.1	31.2	31.2	31.3	31.3	31.3	31.4	31.4	31.5
800	31.5	31.5	31.6	31.6	31.7	31.7	31.7	31.8	31.8	31.9
810	31.9	31.9	32	32	32	32.1	32.1	32.2	32.2	32.2
820	32.3	32.3	32.4	32.4	32.4	32.5	32.5	32.6	32.6	32.6
830	32.7	32.7	32.8	32.8	32.8	32.9	32.9	33	33	33
840	33.1	33.1	33.1	33.2	33.2	33.3	33.3	33.3	33.4	33.4
850	33.5	33.5	33.5	33.6	33.6	33.7	33.7	33.7	33.8	33.8
860	33.9	33.9	33.9	34	34	34.1	34.1	34.1	34.2	34.2
870	34.3	34.3	34.3	34.4	34.4	34.4	34.5	34.5	34.6	34.6
880	34.6	34.7	34.7	34.8	34.8	34.8	34.9	34.9	35	35
890	35	35.1	35.1	35.2	35.2	35.2	35.3	35.3	35.4	35.4
900	35.4	35.5	35.5	35.6	35.6	35.6	35.7	35.7	35.7	35.8
910	35.8	35.9	35.9	35.9	36	36	36.1	36.1	36.1	36.2
920	36.2	36.3	36.3	36.3	36.4	36.4	36.5	36.5	36.5	36.6
930	36.6	36.7	36.7	36.7	36.8	36.8	36.9	36.9	36.9	37
940	37	37	37.1	37.1	37.2	37.2	37.2	37.3	37.3	37.4
950	37.4	37.4	37.5	37.5	37.6	37.6	37.6	37.7	37.7	37.8
960	37.8	37.8	37.9	37.9	38	38	38	38.1	38.1	38.1
970	38.2	38.2	38.3	38.3	38.3	38.4	38.4	38.5	38.5	38.5
980	38.6	38.6	38.7	38.7	38.7	38.8	38.8	38.9	38.9	38.9
990	39	39	39.1	39.1	39.1	39.2	39.2	39.3	39.3	39.3
1000	39.4	39.4	39.4	39.5	39.5	39.6	39.6	39.6	39.7	39.7

Source: engineeringtoolbox.com

Original Source Images

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mm to inches conversion Inches to mm converter

Engineering Notes

Exact definition: Since 1959 the international inch has been defined as exactly 25.4 mm. No rounding is needed for any engineering calculation.
Fractional precision: Fractions such as 1/64 inch carry four decimal places when converted. For most shop-floor work, rounding to two decimal places (0.01 mm) is sufficient.
Tolerance stacking: When converting toleranced dimensions between inch and metric systems, always convert both the nominal value and the tolerance limits independently — do not convert the tolerance band in isolation.
Common confusion: A US survey foot (used in some land-survey contexts) differs slightly from the international foot. This does not affect the inch-to-millimeter relationship but can matter for large-scale coordinate conversions.
Drill and fastener standards: Fractional-inch drill sizes (1/64 through 1 inch in 1/64 increments) and numbered drill sizes (No. 1–80) are defined in ANSI B94.2. Metric equivalents are not always exact matches — consult a cross-reference chart for critical hole fits.
CAD practice: Most modern CAD packages allow dual dimensioning. Set the primary unit to the shop standard and display the secondary unit for international collaborators.

References

Original Source — Engineering ToolBox: Inches to mm Conversion

Source: engineeringtoolbox.com