Cutting Tools Reference Library · Wall Charts

Decimal, Fraction & Millimeter Equivalents

Every 64th of an inch from 1/64 to 1 inch with its decimal and millimeter equivalent.

Ref CT-0055

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A conversion chart for fractional inch sizes in 64ths. Decimals are rounded to four places and millimeters to three. One inch equals exactly 25.4 mm.

How to use it

Find the fraction and read across. To go the other way, find the nearest decimal or millimeter value. For sizes over 1 in, add the whole inches: 1-3/8 in is 1.375 in, or 25.4 + 9.525 = 34.925 mm.

Chart

Fraction (in)	Decimal (in)	Millimeters
1/64	0.0156	0.397
1/32	0.0312	0.794
3/64	0.0469	1.191
1/16	0.0625	1.587
5/64	0.0781	1.984
3/32	0.0938	2.381
7/64	0.1094	2.778
1/8	0.1250	3.175
9/64	0.1406	3.572
5/32	0.1562	3.969
11/64	0.1719	4.366
3/16	0.1875	4.762
13/64	0.2031	5.159
7/32	0.2188	5.556
15/64	0.2344	5.953
1/4	0.2500	6.350
17/64	0.2656	6.747
9/32	0.2812	7.144
19/64	0.2969	7.541
5/16	0.3125	7.938
21/64	0.3281	8.334
11/32	0.3438	8.731
23/64	0.3594	9.128
3/8	0.3750	9.525
25/64	0.3906	9.922
13/32	0.4062	10.319
27/64	0.4219	10.716
7/16	0.4375	11.112
29/64	0.4531	11.509
15/32	0.4688	11.906
31/64	0.4844	12.303
1/2	0.5000	12.700
33/64	0.5156	13.097
17/32	0.5312	13.494
35/64	0.5469	13.891
9/16	0.5625	14.287
37/64	0.5781	14.684
19/32	0.5938	15.081
39/64	0.6094	15.478
5/8	0.6250	15.875
41/64	0.6406	16.272
21/32	0.6562	16.669
43/64	0.6719	17.066
11/16	0.6875	17.462
45/64	0.7031	17.859
23/32	0.7188	18.256
47/64	0.7344	18.653
3/4	0.7500	19.050
49/64	0.7656	19.447
25/32	0.7812	19.844
51/64	0.7969	20.241
13/16	0.8125	20.637
53/64	0.8281	21.034
27/32	0.8438	21.431
55/64	0.8594	21.828
7/8	0.8750	22.225
57/64	0.8906	22.622
29/32	0.9062	23.019
59/64	0.9219	23.416
15/16	0.9375	23.812
61/64	0.9531	24.209
31/32	0.9688	24.606
63/64	0.9844	25.003
1	1.0000	25.400

Key points

Inch to mm: multiply by 25.4. Mm to inch: divide by 25.4.
Decimals are rounded. 1/64 is exactly .015625 in; for close work, carry more places or calculate from the fraction.
Number and letter drills fill the gaps between fractions; see the drill size chart.

Common mistakes

Treating a rounded decimal as exact when stacking tolerances.
Reading 5/32 for 5/16 on a busy chart. Check that the decimal matches.
Assuming a metric drill is a direct substitute for a close fractional size without checking the difference.

Governing standards: None. The inch is defined as exactly 25.4 mm.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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