Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Convert a whole + fraction measurement to decimal inches.
1.5
Equivalent Fractions at Common Denominators
Tape-measure fractions like "1 3/8 inches" aren't directly usable in CAD software, spreadsheets, or digital tools that expect decimal input. This calculator converts a whole-number-plus-fraction measurement into its exact decimal inch equivalent.
Enter the whole-number inches, then the fraction's numerator and denominator (for example, for "1 3/8 inches," enter 1, 3, and 8).
Decimal Inches = Whole Number + (Numerator ÷ Denominator)
| Fraction | Decimal |
|---|---|
| 1/16 | 0.0625 |
| 1/8 | 0.1250 |
| 3/16 | 0.1875 |
| 1/4 | 0.2500 |
| 3/8 | 0.3750 |
| 1/2 | 0.5000 |
| 5/8 | 0.6250 |
| 3/4 | 0.7500 |
| 7/8 | 0.8750 |
Entering a tape-measure reading into CAD software, a cut list spreadsheet, or a 3D printer/CNC program that requires decimal input. Converting a lumber or hardware dimension for calculations that need a precise decimal value.
Read the whole inches first, then count the small marks past that inch. The denominator is set by how finely the tape is divided: sixteenths on a common tape, thirty-seconds on finer rules. Say you measure 3 11/16 in. Enter 3 as the whole number, 11 as the numerator, and 16 as the denominator. The tool computes 3 + 11 ÷ 16 = 3 + 0.6875 = 3.6875 in. Other hypothetical readings: 5/32 in is 0 + 5 ÷ 32 = 0.15625 in, and 7 1/64 in is 7 + 1 ÷ 64 = 7.015625 in.
Every sixteenth adds 0.0625 in, so you can build any sixteenth fraction by multiplying the numerator by 0.0625. Every thirty-second adds 0.03125 in, and every sixty-fourth adds 0.015625 in.
A frequent mistake is misreading the tape. On most tapes, the longest small mark is the half, the next longest is the quarter, then the eighth, and the shortest is the sixteenth. Count from the last whole-inch line and use the full count as the numerator over the subdivision level of the finest mark. If you count 7 sixteenth marks after the 4 in line, enter 4, 7, and 16. It is fine if the fraction is not in lowest terms; 8/16 gives the same decimal as 1/2.
Enter the decimal into CAD software, a spreadsheet, or a CNC program. Many of these tools accept three or four decimal places, so the long decimals here are usually fine. If a program has a limit, round to the required precision. For example, 0.15625 rounded to three decimals is 0.156, a difference of about 0.0003 in.
1 + (3 ÷ 8) = 1.375 inches.
Enter 0 for the whole number field -- for example, "7/8 inch" would be 0 whole, numerator 7, denominator 8, giving 0.875in.
5 ÷ 16 = 0.3125 in.
Yes. With whole = 0, 19/16 gives 1.1875 in, the same as 1 3/16.
For woodworking, three decimals are typically plenty. For machining, follow your drawing's stated tolerance.
Use the Inches to Fraction Calculator, which rounds a decimal to the nearest fraction at your chosen denominator.
Reference: NIST Weights and Measures