FractionReference

Fraction → metric chart

Every 64th of an inch with its exact millimetre value. The coarser rules are all in here — the reduced column shows where 16/64 becomes 1/4.

64ths Reduced Decimal mm
1/64 — 0.015625 0.396875
2/64 1/32 0.03125 0.79375
3/64 — 0.046875 1.190625
4/64 1/16 0.0625 1.5875
5/64 — 0.078125 1.984375
6/64 3/32 0.09375 2.38125
7/64 — 0.109375 2.778125
8/64 1/8 0.125 3.175
9/64 — 0.140625 3.571875
10/64 5/32 0.15625 3.96875
11/64 — 0.171875 4.365625
12/64 3/16 0.1875 4.7625
13/64 — 0.203125 5.159375
14/64 7/32 0.21875 5.55625
15/64 — 0.234375 5.953125
16/64 1/4 0.25 6.35
17/64 — 0.265625 6.746875
18/64 9/32 0.28125 7.14375
19/64 — 0.296875 7.540625
20/64 5/16 0.3125 7.9375
21/64 — 0.328125 8.334375
22/64 11/32 0.34375 8.73125
23/64 — 0.359375 9.128125
24/64 3/8 0.375 9.525
25/64 — 0.390625 9.921875
26/64 13/32 0.40625 10.31875
27/64 — 0.421875 10.715625
28/64 7/16 0.4375 11.1125
29/64 — 0.453125 11.509375
30/64 15/32 0.46875 11.90625
31/64 — 0.484375 12.303125
32/64 1/2 0.5 12.7
64ths Reduced Decimal mm
33/64 — 0.515625 13.096875
34/64 17/32 0.53125 13.49375
35/64 — 0.546875 13.890625
36/64 9/16 0.5625 14.2875
37/64 — 0.578125 14.684375
38/64 19/32 0.59375 15.08125
39/64 — 0.609375 15.478125
40/64 5/8 0.625 15.875
41/64 — 0.640625 16.271875
42/64 21/32 0.65625 16.66875
43/64 — 0.671875 17.065625
44/64 11/16 0.6875 17.4625
45/64 — 0.703125 17.859375
46/64 23/32 0.71875 18.25625
47/64 — 0.734375 18.653125
48/64 3/4 0.75 19.05
49/64 — 0.765625 19.446875
50/64 25/32 0.78125 19.84375
51/64 — 0.796875 20.240625
52/64 13/16 0.8125 20.6375
53/64 — 0.828125 21.034375
54/64 27/32 0.84375 21.43125
55/64 — 0.859375 21.828125
56/64 7/8 0.875 22.225
57/64 — 0.890625 22.621875
58/64 29/32 0.90625 23.01875
59/64 — 0.921875 23.415625
60/64 15/16 0.9375 23.8125
61/64 — 0.953125 24.209375
62/64 31/32 0.96875 24.60625
63/64 — 0.984375 25.003125
64/64 1 1 25.4

Common questions

How were the millimetre values computed?
By multiplying each fraction by 25.4 — the exact definition of the inch since 1959. Every mm value on this chart is exact, not rounded: 1/64″ is 0.396875 mm, to the last digit.
Why 64ths?
The 64ths grid contains every coarser rule — halves, quarters, eighths, 16ths and 32nds all land on 64th marks — so one chart covers them all, with the reduced form shown beside each.
Where this comes from. Exact rational arithmetic on the values shown — fractions are pairs of integers until display, and inch–metric conversion uses 25.4 mm to the inch, exact by definition since 1959. See the full methodology.