Decimal Equivalent Chart
This chart lists all 64 inch-fraction graduations from 1/64" to 1", each with its exact decimal and millimetre value. 1/64" = 0.015625" = 0.396875 mm, and every other line follows the same pattern up to a full inch.
Every 64th, Simplified
A decimal equivalent chart lines up every fractional-inch graduation with its exact decimal and millimetre value, so you can go from any one notation to the other two without doing the arithmetic yourself.
The chart runs in steps of 1/64", the finest common graduation on a machinist's rule, but most of those 64 positions land on a simpler fraction — 32/64 is really 1/2, and 16/64 is really 1/4. Every row below shows the fraction already reduced to its simplest form, exactly the way it would be labeled on a physical rule.
How Each Row Is Calculated
Two formulas generate every value on this chart from the row's position, n, out of 64.
D is the decimal value of the nth sixty-fourth. MM is that same fraction converted to millimetres.
- nThe row number, from 1 to 64.
- DThe decimal value: n ÷ 64.
- MMThe millimetre value: (n × 25.4) ÷ 64.
Worked calculation — n = 25
- 25 ÷ 64 = 0.390625Decimal value
- 25 × 25.4 = 635Multiply by mm-per-inch
- 635 ÷ 64 = 9.921875Divide by 64 for millimetres
25/64" = 0.390625" = 9.921875 mm
All 64 Fractions, 1/64" to 1"
Every graduation from 1/64" to a full inch, in two side-by-side columns for a compact, printable layout.
| Fraction | Decimal | MM | Fraction | Decimal | MM |
|---|---|---|---|---|---|
| 1/64" | 0.015625" | 0.3969 | 33/64" | 0.515625" | 13.0969 |
| 1/32" | 0.03125" | 0.7937 | 17/32" | 0.53125" | 13.4937 |
| 3/64" | 0.046875" | 1.1906 | 35/64" | 0.546875" | 13.8906 |
| 1/16" | 0.0625" | 1.5875 | 9/16" | 0.5625" | 14.2875 |
| 5/64" | 0.078125" | 1.9844 | 37/64" | 0.578125" | 14.6844 |
| 3/32" | 0.09375" | 2.3812 | 19/32" | 0.59375" | 15.0812 |
| 7/64" | 0.109375" | 2.7781 | 39/64" | 0.609375" | 15.4781 |
| 1/8" | 0.125" | 3.175 | 5/8" | 0.625" | 15.875 |
| 9/64" | 0.140625" | 3.5719 | 41/64" | 0.640625" | 16.2719 |
| 5/32" | 0.15625" | 3.9688 | 21/32" | 0.65625" | 16.6687 |
| 11/64" | 0.171875" | 4.3656 | 43/64" | 0.671875" | 17.0656 |
| 3/16" | 0.1875" | 4.7625 | 11/16" | 0.6875" | 17.4625 |
| 13/64" | 0.203125" | 5.1594 | 45/64" | 0.703125" | 17.8594 |
| 7/32" | 0.21875" | 5.5562 | 23/32" | 0.71875" | 18.2562 |
| 15/64" | 0.234375" | 5.9531 | 47/64" | 0.734375" | 18.6531 |
| 1/4" | 0.25" | 6.35 | 3/4" | 0.75" | 19.05 |
| 17/64" | 0.265625" | 6.7469 | 49/64" | 0.765625" | 19.4469 |
| 9/32" | 0.28125" | 7.1437 | 25/32" | 0.78125" | 19.8438 |
| 19/64" | 0.296875" | 7.5406 | 51/64" | 0.796875" | 20.2406 |
| 5/16" | 0.3125" | 7.9375 | 13/16" | 0.8125" | 20.6375 |
| 21/64" | 0.328125" | 8.3344 | 53/64" | 0.828125" | 21.0344 |
| 11/32" | 0.34375" | 8.7312 | 27/32" | 0.84375" | 21.4312 |
| 23/64" | 0.359375" | 9.1281 | 55/64" | 0.859375" | 21.8281 |
| 3/8" | 0.375" | 9.525 | 7/8" | 0.875" | 22.225 |
| 25/64" | 0.390625" | 9.9219 | 57/64" | 0.890625" | 22.6219 |
| 13/32" | 0.40625" | 10.3187 | 29/32" | 0.90625" | 23.0187 |
| 27/64" | 0.421875" | 10.7156 | 59/64" | 0.921875" | 23.4156 |
| 7/16" | 0.4375" | 11.1125 | 15/16" | 0.9375" | 23.8125 |
| 29/64" | 0.453125" | 11.5094 | 61/64" | 0.953125" | 24.2094 |
| 15/32" | 0.46875" | 11.9063 | 31/32" | 0.96875" | 24.6062 |
| 31/64" | 0.484375" | 12.3031 | 63/64" | 0.984375" | 25.0031 |
| 1/2" | 0.5" | 12.7 | 1/1" | 1" | 25.4 |
Using the Chart on the Shop Floor
- Starting from a fraction? Scan the fraction columns for your value and read across for the decimal and millimetre equivalents.
- Starting from a decimal or a caliper reading? Scan the decimal columns for the closest match — the chart is ordered, so the nearest row is easy to spot.
- Starting from a metric spec? Scan the millimetre columns the same way, then read back to find the nearest standard fraction.
Frequently Asked Questions
What is 1/64 of an inch in decimal?
1/64" equals 0.015625" as a decimal — the finest increment shown on this chart, found by dividing 1 by 64.
Why does the chart stop at 64ths?
Sixty-fourths of an inch is the finest graduation found on most machinist rules and shop reference charts in everyday use. Finer divisions, such as 128ths, exist but are rare outside specialized tooling.
How do you read a decimal equivalent chart?
Find your fraction, already reduced to its simplest form, in the left column — or find the closest decimal value in the middle column if that's what you're starting from — then read the matching millimetre value on the right for the metric equivalent.
What is 25/64 in mm?
25/64" equals 9.921875 mm, found by multiplying 25 by 25.4 and dividing by 64: (25 × 25.4) ÷ 64 = 635 ÷ 64 = 9.921875.
Is this chart the same as a drill size chart?
No. A drill size chart cross-references fractional sizes against lettered (A–Z) and numbered (#1–#80) drill bit sizes, which don't run in a simple numeric sequence. This decimal equivalent chart covers only the fraction-to-decimal-to-millimetre relationship, without any drill-specific data — see the <a href="/drill-chart/">drill size decimal chart</a> for that cross-reference.
Reference Charts
Every other chart in this cluster, one click away.