Inches to Fraction Calculator — Decimal to Fractional Inches
Enter a decimal inch measurement (e.g. 1.375) and choose your precision (1/8, 1/16, 1/32, or 1/64 of an inch) to get the nearest fractional representation used in woodworking, carpentry and machining drawings.
in
Precision (smallest fraction)
How does this calculator work?
Multiply the decimal fractional part by the denominator you want (e.g. ×8 for eighths), round to the nearest integer, and that is the numerator. Simplify by dividing numerator and denominator by their GCD. Example: 1.375 → fractional part 0.375 × 8 = 3 → 1 3/8" (exact, zero error).
Formula
How this is calculated
Imperial measurements on drawings and in workshop practice are often expressed as mixed fractions of an inch rather than decimals: 1 3/8" or 5/16" instead of 1.375" or 0.3125". The conversion works by separating the decimal into its whole-number part and its fractional part, then rounding the fractional part to the nearest multiple of 1/denominator.
For example, 1.375 with denominator 8: the fractional part is 0.375; multiplied by 8 gives 3.0 exactly, so the result is 3/8 with zero rounding error. With denominator 16, 0.375 × 16 = 6.0, giving 6/16 = 3/8 again. With denominator 4, 0.375 × 4 = 1.5, which rounds to 2/4 = 1/2" (error = 0.125"). The GCD step simplifies the fraction to its lowest terms.
Choose the denominator to match the precision of your tool or drawing: woodworking drawings typically use 1/16", precision machining 1/64", rough carpentry 1/8". The rounding error is shown so you can judge whether the approximation is acceptable for your application. An error of more than 0.5 mm (0.020") is usually significant in joinery.
Frequently asked questions
0.375 = 3/8 (exactly). Multiply 0.375 × 8 = 3, so 3/8 with zero rounding error. Similarly 0.125 = 1/8, 0.25 = 1/4, 0.5 = 1/2, 0.0625 = 1/16.
Most woodworking drawings use 1/16" or 1/32" precision. High-end joinery and cabinetmaking may specify 1/32". Basic rough carpentry is usually 1/8". Precision machining drawings commonly use 1/64" as the finest standard fraction.
The calculator rounds to the nearest fraction at your chosen precision and shows the rounding error in both inches and millimetres. If the error matters, increase the denominator (finer precision) or consider whether a decimal or metric specification would better suit your use case.
Also known as
TG we-Calculate Editorial Team. (2026). Inches to Fraction Calculator — Decimal to Fractional Inches [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/inches-to-fraction-calculator
TG we-Calculate Editorial Team. "Inches to Fraction Calculator — Decimal to Fractional Inches." TG we-Calculate. 2026. https://we-calculate.com/calculator/inches-to-fraction-calculator.
TG we-Calculate Editorial Team, "Inches to Fraction Calculator — Decimal to Fractional Inches," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/inches-to-fraction-calculator
@misc{wecalculate_inches_to_fraction_calculator, title = {Inches to Fraction Calculator — Decimal to Fractional Inches}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/inches-to-fraction-calculator}}, year = {2026}, note = {TG we-Calculate} }
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