Reference · Measurement
Inch Fraction to Decimal Chart
Updated: June 2026
Tape measures speak in fractions — sixteenths and thirty-seconds — but calipers, CNC machines and spreadsheets speak in decimals. This chart bridges the two so you can move a measurement from the workshop to the screen without second-guessing, whether you work in woodworking, metalworking or DIY.
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How inch fractions become decimals
Every inch fraction is a division, exactly like any other fraction. A sixteenth is 1 ÷ 16 = 0.0625 inch. Because the denominators are all powers of two, every one of these decimals terminates cleanly — there are no repeating decimals on a tape measure.
1/8 = 0.125"
1/4 = 0.25"
1/2 = 0.5"
Each step up the tape adds another 0.0625 inch, so reading a tape in decimals is just counting sixteenths and multiplying.
Common fractions chart
| Fraction (in) | Decimal (in) | Millimetres |
|---|---|---|
| 1/16 | 0.0625 | 1.588 |
| 1/8 | 0.125 | 3.175 |
| 3/16 | 0.1875 | 4.763 |
| 1/4 | 0.25 | 6.35 |
| 5/16 | 0.3125 | 7.938 |
| 3/8 | 0.375 | 9.525 |
| 7/16 | 0.4375 | 11.113 |
| 1/2 | 0.5 | 12.7 |
| 9/16 | 0.5625 | 14.288 |
| 5/8 | 0.625 | 15.875 |
| 3/4 | 0.75 | 19.05 |
| 7/8 | 0.875 | 22.225 |
To get millimetres, multiply the decimal inch by 25.4, since one inch is defined as exactly 25.4 mm.
Reading a tape measure
The longest marks are inches and half-inches; the shorter the line, the finer the fraction. A standard tape divides each inch into sixteenths. Count the sixteenths from the last whole inch, then look the fraction up or multiply by 0.0625. Three marks past the 4-inch line is 3/16, so 4 3/16 inches is 4.1875 inches.
Down to thirty-seconds and sixty-fourths
Machinists often need finer steps. The pattern continues: a thirty-second is 0.03125 inch, a sixty-fourth is 0.015625 inch. Each halving of the fraction halves the decimal too, which makes the whole system easy to extend without a chart in hand.
1/64 = 0.015625"
3/64 = 0.046875"
Rounding for the real world
Calipers usually read to three decimal places (thousandths of an inch, called “thou”), so 0.0625 shows as 0.063. For most woodworking, two decimals is plenty. Decide your tolerance first, then round — a cabinet door does not need machinist precision, and a bearing seat does. Keeping the exact fraction alongside the rounded decimal saves you from stacking rounding errors across several cuts.
Frequently asked questions
What is 1/16 inch in decimal?
1/16 inch is 0.0625 inch, or about 1.59 mm.
How do I convert inch fractions to millimetres?
Convert the fraction to a decimal inch, then multiply by 25.4, since one inch equals 25.4 mm.
Why do tape-measure fractions always terminate?
Their denominators are powers of two (2, 4, 8, 16, 32, 64), so the decimals always stop and never repeat.