Fraction to Decimal Inch Chart (with Millimeters)

US measurements use fractions of an inch, while drawings, calipers and product specs often use decimals or millimeters. This chart converts between all three. One inch is exactly 25.4 mm, so every value below is exact, not rounded from a lookup table.

Common fractions (1/16 inch steps)

Fraction (in)	Decimal (in)	Millimeters
1/16	0.0625	1.587
1/8	0.1250	3.175
3/16	0.1875	4.762
1/4	0.2500	6.350
5/16	0.3125	7.938
3/8	0.3750	9.525
7/16	0.4375	11.112
1/2	0.5000	12.700
9/16	0.5625	14.287
5/8	0.6250	15.875
11/16	0.6875	17.462
3/4	0.7500	19.050
13/16	0.8125	20.637
7/8	0.8750	22.225
15/16	0.9375	23.812
1	1.0000	25.400

Full chart (1/64 inch steps)

Fraction (in)	Decimal (in)	Millimeters
1/64	0.015625	0.3969
1/32	0.031250	0.7937
3/64	0.046875	1.1906
1/16	0.062500	1.5875
5/64	0.078125	1.9844
3/32	0.093750	2.3812
7/64	0.109375	2.7781
1/8	0.125000	3.1750
9/64	0.140625	3.5719
5/32	0.156250	3.9688
11/64	0.171875	4.3656
3/16	0.187500	4.7625
13/64	0.203125	5.1594
7/32	0.218750	5.5562
15/64	0.234375	5.9531
1/4	0.250000	6.3500
17/64	0.265625	6.7469
9/32	0.281250	7.1437
19/64	0.296875	7.5406
5/16	0.312500	7.9375
21/64	0.328125	8.3344
11/32	0.343750	8.7312
23/64	0.359375	9.1281
3/8	0.375000	9.5250
25/64	0.390625	9.9219
13/32	0.406250	10.3187
27/64	0.421875	10.7156
7/16	0.437500	11.1125
29/64	0.453125	11.5094
15/32	0.468750	11.9062
31/64	0.484375	12.3031
1/2	0.500000	12.7000
33/64	0.515625	13.0969
17/32	0.531250	13.4937
35/64	0.546875	13.8906
9/16	0.562500	14.2875
37/64	0.578125	14.6844
19/32	0.593750	15.0812
39/64	0.609375	15.4781
5/8	0.625000	15.8750
41/64	0.640625	16.2719
21/32	0.656250	16.6687
43/64	0.671875	17.0656
11/16	0.687500	17.4625
45/64	0.703125	17.8594
23/32	0.718750	18.2562
47/64	0.734375	18.6531
3/4	0.750000	19.0500
49/64	0.765625	19.4469
25/32	0.781250	19.8438
51/64	0.796875	20.2406
13/16	0.812500	20.6375
53/64	0.828125	21.0344
27/32	0.843750	21.4312
55/64	0.859375	21.8281
7/8	0.875000	22.2250
57/64	0.890625	22.6219
29/32	0.906250	23.0187
59/64	0.921875	23.4156
15/16	0.937500	23.8125
61/64	0.953125	24.2094
31/32	0.968750	24.6062
63/64	0.984375	25.0031
1	1.000000	25.4000

How to convert a fraction to a decimal

Divide the top number by the bottom number. For 5/8, 5 ÷ 8 = 0.625 inch. To get millimeters, multiply the decimal by 25.4: 0.625 × 25.4 = 15.875 mm.

For a mixed number such as 2 3/4 inches, convert the fraction and add the whole number: 3 ÷ 4 = 0.75, so it’s 2.75 inches or 69.85 mm.

How to convert a decimal to a fraction

1. Decide how precise you need to be. Sixteenths are standard for tape measures and most rulers.
2. Multiply the decimal part by 16 (or 32, or 64) and round to a whole number.
3. Write the result over 16 and simplify.

Example: 0.4 inch → 0.4 × 16 = 6.4 → rounds to 6 → 6/16 → 3/8 inch. Check it in the chart: 3/8 is 0.375, the closest sixteenth to 0.4. To skip the arithmetic, the drill size calculator will round any decimal to the nearest 1/64 inch and show the closest drill bit.

Converting millimeters to inch fractions

Divide millimeters by 25.4 to get decimal inches, then use the steps above. For example, 10 mm ÷ 25.4 = 0.3937 inch, which is closest to 25/64 (0.3906) or, in sixteenths, 6/16 = 3/8 (0.375).

If you’re reading a physical ruler, our guide on how to read a ruler shows which line is which fraction. To measure small parts directly in millimeters, use the mm ruler on your screen.