Tape Measure Fractions to Decimals and Millimeters, Plus Cutting Lists With Kerf
October 29, 2026
Tape measures mark inches in halves, quarters, eighths, sixteenths, and sometimes thirty-seconds. To use them with calipers, spreadsheets, or metric tools, convert fractions to decimals by dividing the numerator by the denominator: 5/16 = 5 ÷ 16 = 0.3125 inch. Multiply by 25.4 to get millimeters: 0.3125 × 25.4 = 7.94 mm.
Other examples: 11/32 = 0.34375 inch (8.73 mm); 13/64 = 0.203125 inch (5.16 mm); 7/8 = 0.875 inch (22.23 mm); 1/64 = 0.015625 inch (0.397 mm).
Skip the math and get your answer instantly:
Open the Fraction Calculator →Conversion Chart
The 16ths are the ones most used. Each 1/16 inch is 0.0625 inch or 1.5875 mm. A handy check: 1/8 = 0.125, 1/4 = 0.25, 3/8 = 0.375, 1/2 = 0.5, 5/8 = 0.625, 3/4 = 0.75, 7/8 = 0.875. To convert a decimal back to a fraction, multiply the decimal part by the denominator you want and round: 0.4 inch × 32 = 12.8, which rounds to 13, so 0.4 inch is about 13/32 (0.40625). Use the denominator that matches the precision of your tape.
| Fraction | Decimal (inch) | Millimeters |
|---|---|---|
| 1/16 | 0.0625 | 1.59 |
| 1/8 | 0.125 | 3.18 |
| 5/16 | 0.3125 | 7.94 |
| 3/8 | 0.375 | 9.53 |
| 1/2 | 0.5 | 12.70 |
| 5/8 | 0.625 | 15.88 |
| 3/4 | 0.75 | 19.05 |
| 7/8 | 0.875 | 22.23 |
Adding Fractions on a Cutting List
To add 31 5/8 inch three times: 3 × 31.625 = 94.875 inches. A saw blade removes a strip of material called the kerf, typically 1/8 inch (0.125) for a standard blade. Cutting three pieces from one 96-inch board takes two cuts between the pieces, the third piece ends at the board's end, so the total used is 94.875 + 2 × 0.125 = 95.125 inches, leaving 96 − 95.125 = 0.875 inch, or 7/8 inch, as an offcut. If you needed four pieces of this length, you couldn't get them from one board. Always include the kerf for each cut when planning; with a thin-kerf blade (3/32 = 0.094 inch) you save a bit.
Tips for Accuracy
Measure from the same reference edge and mark with a knife or a sharp pencil. Add up all of the cut lengths and kerfs before purchasing material, and add 10% extra for mistakes and defects. When working across metric and imperial plans, convert once and round to the precision of the tool: 1/32 inch is about 0.8 mm, adequate for most carpentry. For precision joinery, use decimal inches or millimeters on calipers.
Common Mistakes
Reading the wrong tick mark, forgetting that the hook on the tape end moves slightly to compensate for its thickness, and mixing mixed numbers incorrectly (3 1/2 means 3.5, not 3 + 1/2 × something else). Convert everything to decimals before adding, then convert back for marking.
Frequently Asked Questions
How do I convert a fraction of an inch to decimal?
Divide the numerator by the denominator.
How do I convert inches to millimeters?
Multiply by 25.4.
What is saw kerf?
The width of material removed by the blade, typically about 1/8 inch.
How many cuts for three pieces from a board?
Two cuts between the pieces, plus the board's end.
How much extra material should I buy?
About 10% for mistakes and defects.