How it works
Ruler ticks = round(inches × denominator). Fraction = ticks ÷ denominator. Millimetres = inches × 25.4.
- Choose decimal inches, mm or fraction input.
- Enter your length.
- Choose a ruler precision.
- Read the fraction and signed rounding error.
Worked example: 2.65 × 16 = 42.4, which rounds to 42, so 42/16 = 2 5/8. The rounded length is 2.625 inches, 0.025 inches below the input.
Sixteenth-inch reference table
| Fraction | Decimal inches | Millimetres |
|---|---|---|
| 1/16″ | 0.0625 | 1.5875 |
| 1/8″ | 0.125 | 3.175 |
| 3/16″ | 0.1875 | 4.7625 |
| 1/4″ | 0.25 | 6.35 |
| 5/16″ | 0.3125 | 7.9375 |
| 3/8″ | 0.375 | 9.525 |
| 7/16″ | 0.4375 | 11.1125 |
| 1/2″ | 0.5 | 12.7 |
| 9/16″ | 0.5625 | 14.2875 |
| 5/8″ | 0.625 | 15.875 |
| 11/16″ | 0.6875 | 17.4625 |
| 3/4″ | 0.75 | 19.05 |
| 13/16″ | 0.8125 | 20.6375 |
| 7/8″ | 0.875 | 22.225 |
| 15/16″ | 0.9375 | 23.8125 |
| 1″ | 1 | 25.4 |
Swipe the table sideways to see the rest.
Exact lengths for all marks from 1/16 inch to 1 inch.
1/64 inch reference table
| Fraction | Decimal inches | Millimetres |
|---|---|---|
| 1/64″ | 0.015625 | 0.396875 |
| 1/32″ | 0.03125 | 0.79375 |
| 3/64″ | 0.046875 | 1.190625 |
| 1/16″ | 0.0625 | 1.5875 |
| 5/64″ | 0.078125 | 1.984375 |
| 3/32″ | 0.09375 | 2.38125 |
| 7/64″ | 0.109375 | 2.778125 |
| 1/8″ | 0.125 | 3.175 |
| 9/64″ | 0.140625 | 3.571875 |
| 5/32″ | 0.15625 | 3.96875 |
| 11/64″ | 0.171875 | 4.365625 |
| 3/16″ | 0.1875 | 4.7625 |
| 13/64″ | 0.203125 | 5.159375 |
| 7/32″ | 0.21875 | 5.55625 |
| 15/64″ | 0.234375 | 5.953125 |
| 1/4″ | 0.25 | 6.35 |
| 17/64″ | 0.265625 | 6.746875 |
| 9/32″ | 0.28125 | 7.14375 |
| 19/64″ | 0.296875 | 7.540625 |
| 5/16″ | 0.3125 | 7.9375 |
| 21/64″ | 0.328125 | 8.334375 |
| 11/32″ | 0.34375 | 8.73125 |
| 23/64″ | 0.359375 | 9.128125 |
| 3/8″ | 0.375 | 9.525 |
| 25/64″ | 0.390625 | 9.921875 |
| 13/32″ | 0.40625 | 10.31875 |
| 27/64″ | 0.421875 | 10.715625 |
| 7/16″ | 0.4375 | 11.1125 |
| 29/64″ | 0.453125 | 11.509375 |
| 15/32″ | 0.46875 | 11.90625 |
| 31/64″ | 0.484375 | 12.303125 |
| 1/2″ | 0.5 | 12.7 |
| 33/64″ | 0.515625 | 13.096875 |
| 17/32″ | 0.53125 | 13.49375 |
| 35/64″ | 0.546875 | 13.890625 |
| 9/16″ | 0.5625 | 14.2875 |
| 37/64″ | 0.578125 | 14.684375 |
| 19/32″ | 0.59375 | 15.08125 |
| 39/64″ | 0.609375 | 15.478125 |
| 5/8″ | 0.625 | 15.875 |
| 41/64″ | 0.640625 | 16.271875 |
| 21/32″ | 0.65625 | 16.66875 |
| 43/64″ | 0.671875 | 17.065625 |
| 11/16″ | 0.6875 | 17.4625 |
| 45/64″ | 0.703125 | 17.859375 |
| 23/32″ | 0.71875 | 18.25625 |
| 47/64″ | 0.734375 | 18.653125 |
| 3/4″ | 0.75 | 19.05 |
| 49/64″ | 0.765625 | 19.446875 |
| 25/32″ | 0.78125 | 19.84375 |
| 51/64″ | 0.796875 | 20.240625 |
| 13/16″ | 0.8125 | 20.6375 |
| 53/64″ | 0.828125 | 21.034375 |
| 27/32″ | 0.84375 | 21.43125 |
| 55/64″ | 0.859375 | 21.828125 |
| 7/8″ | 0.875 | 22.225 |
| 57/64″ | 0.890625 | 22.621875 |
| 29/32″ | 0.90625 | 23.01875 |
| 59/64″ | 0.921875 | 23.415625 |
| 15/16″ | 0.9375 | 23.8125 |
| 61/64″ | 0.953125 | 24.209375 |
| 31/32″ | 0.96875 | 24.60625 |
| 63/64″ | 0.984375 | 25.003125 |
| 1″ | 1 | 25.4 |
Things to consider
- Use finer marks only when you can measure them.
- Keep decimals for precision calculations.
- Check the rounding error before cutting.
- Use the original decimal, not a rounded fraction, for further conversions.
Frequently asked questions
How do I convert a decimal to an inch fraction?
Multiply decimal inches by the denominator, round to the nearest whole mark and divide by the denominator. Simplify the fraction and separate whole inches. At 1/16, 2.65 rounds to 42/16, or 2 5/8 inches. A fraction reaching the next whole inch carries correctly.
How do I read a tape measure?
Start with whole inches, then count marks after that inch. On a sixteenth-inch scale, each small mark is 1/16. Longer marks often indicate halves, quarters and eighths. Eight sixteenths simplifies to 1/2. Check the divisions on your own tape.
Which precision should I use?
A sixteenth is common for woodworking, but the right precision depends on the job and measuring tool. Machining usually uses decimal dimensions and specified tolerances rather than rounded ruler fractions. Finer fractions do not make a measurement more accurate by themselves.
How do I convert mm to fractional inches?
Divide mm by exactly 25.4, then round to your chosen inch fraction. Ten mm is about 0.3937 inches and rounds to 3/8 at 1/16 precision. For centimetres, use the Centimetres to Inches Converter. A mil is not a millimetre; use the Mils to Inches Converter for mils.
Why are some decimals not exact ruler fractions?
Ruler marks with denominators 2, 4, 8, 16, 32 or 64 only represent certain values. For example, 0.375 is exactly 3/8, but 0.3 lies between marks. The exactness result compares the original value with the selected mark using exact arithmetic, not the displayed rounded decimals.
Results are estimates for general information only, not financial, medical or professional advice.