FractionReference / Charts / 128ths 128ths of an inch
As fine as fractional measurement goes — beyond this, the trade speaks in decimal
thousandths. Every mark, with its reduced name, exact decimal and exact millimetres.
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128ths Reduced Decimal mm 1/128 — 0.0078125 0.1984375 2/128 1/64 0.015625 0.396875 3/128 — 0.0234375 0.5953125 4/128 1/32 0.03125 0.79375 5/128 — 0.0390625 0.9921875 6/128 3/64 0.046875 1.190625 7/128 — 0.0546875 1.3890625 8/128 1/16 0.0625 1.5875 9/128 — 0.0703125 1.7859375 10/128 5/64 0.078125 1.984375 11/128 — 0.0859375 2.1828125 12/128 3/32 0.09375 2.38125 13/128 — 0.1015625 2.5796875 14/128 7/64 0.109375 2.778125 15/128 — 0.1171875 2.9765625 16/128 1/8 0.125 3.175 17/128 — 0.1328125 3.3734375 18/128 9/64 0.140625 3.571875 19/128 — 0.1484375 3.7703125 20/128 5/32 0.15625 3.96875 21/128 — 0.1640625 4.1671875 22/128 11/64 0.171875 4.365625 23/128 — 0.1796875 4.5640625 24/128 3/16 0.1875 4.7625 25/128 — 0.1953125 4.9609375 26/128 13/64 0.203125 5.159375 27/128 — 0.2109375 5.3578125 28/128 7/32 0.21875 5.55625 29/128 — 0.2265625 5.7546875 30/128 15/64 0.234375 5.953125 31/128 — 0.2421875 6.1515625 32/128 1/4 0.25 6.35
128ths Reduced Decimal mm 33/128 — 0.2578125 6.5484375 34/128 17/64 0.265625 6.746875 35/128 — 0.2734375 6.9453125 36/128 9/32 0.28125 7.14375 37/128 — 0.2890625 7.3421875 38/128 19/64 0.296875 7.540625 39/128 — 0.3046875 7.7390625 40/128 5/16 0.3125 7.9375 41/128 — 0.3203125 8.1359375 42/128 21/64 0.328125 8.334375 43/128 — 0.3359375 8.5328125 44/128 11/32 0.34375 8.73125 45/128 — 0.3515625 8.9296875 46/128 23/64 0.359375 9.128125 47/128 — 0.3671875 9.3265625 48/128 3/8 0.375 9.525 49/128 — 0.3828125 9.7234375 50/128 25/64 0.390625 9.921875 51/128 — 0.3984375 10.1203125 52/128 13/32 0.40625 10.31875 53/128 — 0.4140625 10.5171875 54/128 27/64 0.421875 10.715625 55/128 — 0.4296875 10.9140625 56/128 7/16 0.4375 11.1125 57/128 — 0.4453125 11.3109375 58/128 29/64 0.453125 11.509375 59/128 — 0.4609375 11.7078125 60/128 15/32 0.46875 11.90625 61/128 — 0.4765625 12.1046875 62/128 31/64 0.484375 12.303125 63/128 — 0.4921875 12.5015625 64/128 1/2 0.5 12.7
128ths Reduced Decimal mm 65/128 — 0.5078125 12.8984375 66/128 33/64 0.515625 13.096875 67/128 — 0.5234375 13.2953125 68/128 17/32 0.53125 13.49375 69/128 — 0.5390625 13.6921875 70/128 35/64 0.546875 13.890625 71/128 — 0.5546875 14.0890625 72/128 9/16 0.5625 14.2875 73/128 — 0.5703125 14.4859375 74/128 37/64 0.578125 14.684375 75/128 — 0.5859375 14.8828125 76/128 19/32 0.59375 15.08125 77/128 — 0.6015625 15.2796875 78/128 39/64 0.609375 15.478125 79/128 — 0.6171875 15.6765625 80/128 5/8 0.625 15.875 81/128 — 0.6328125 16.0734375 82/128 41/64 0.640625 16.271875 83/128 — 0.6484375 16.4703125 84/128 21/32 0.65625 16.66875 85/128 — 0.6640625 16.8671875 86/128 43/64 0.671875 17.065625 87/128 — 0.6796875 17.2640625 88/128 11/16 0.6875 17.4625 89/128 — 0.6953125 17.6609375 90/128 45/64 0.703125 17.859375 91/128 — 0.7109375 18.0578125 92/128 23/32 0.71875 18.25625 93/128 — 0.7265625 18.4546875 94/128 47/64 0.734375 18.653125 95/128 — 0.7421875 18.8515625 96/128 3/4 0.75 19.05
128ths Reduced Decimal mm 97/128 — 0.7578125 19.2484375 98/128 49/64 0.765625 19.446875 99/128 — 0.7734375 19.6453125 100/128 25/32 0.78125 19.84375 101/128 — 0.7890625 20.0421875 102/128 51/64 0.796875 20.240625 103/128 — 0.8046875 20.4390625 104/128 13/16 0.8125 20.6375 105/128 — 0.8203125 20.8359375 106/128 53/64 0.828125 21.034375 107/128 — 0.8359375 21.2328125 108/128 27/32 0.84375 21.43125 109/128 — 0.8515625 21.6296875 110/128 55/64 0.859375 21.828125 111/128 — 0.8671875 22.0265625 112/128 7/8 0.875 22.225 113/128 — 0.8828125 22.4234375 114/128 57/64 0.890625 22.621875 115/128 — 0.8984375 22.8203125 116/128 29/32 0.90625 23.01875 117/128 — 0.9140625 23.2171875 118/128 59/64 0.921875 23.415625 119/128 — 0.9296875 23.6140625 120/128 15/16 0.9375 23.8125 121/128 — 0.9453125 24.0109375 122/128 61/64 0.953125 24.209375 123/128 — 0.9609375 24.4078125 124/128 31/32 0.96875 24.60625 125/128 — 0.9765625 24.8046875 126/128 63/64 0.984375 25.003125 127/128 — 0.9921875 25.2015625 128/128 1 1 25.4
Coarser rules: 16ths · 32nds · 64ths
Common questions Does anyone actually measure in 128ths? Rarely by eye — a 128th is about 0.2 mm, finer than most rules are engraved. The grid matters as a boundary: it is the last fractional step before work moves to decimal inches and thousandths. How big is 1/128 of an inch in millimetres? 1/128″ is exactly 0.1984375 mm. Every mm value on this chart is exact, at 25.4 mm to the inch. 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 . 
Fraction