Inches to Fraction Calculator

Shop drawings and CNC programs often use decimal inches, while carpenters and machinists still prefer fractions like 5/32 or 1/64. This calculator normalizes any input (decimal inches or metric) into meters, converts to inches, then rounds to the nearest fraction using whatever denominator (up to 1/64) you specify.

How the conversion works

• Convert your entry to pure inches ($\text{in} = \tfrac{\text{mm}}{25.4}$ or decimal inches directly).
• Multiply the fractional portion by the chosen denominator (e.g., 64), round to the nearest whole number, and simplify the fraction.

The whole inches stay intact while the remainder becomes a numerator over the selected denominator.

Units and conversions

Worked examples

1. Decimal to fraction
   Convert 2.375 in to a 1/64-based fraction.

$$0.375 \times 64 = 24 \Rightarrow 2\,\tfrac{24}{64} = 2\,\tfrac{3}{8}$$

Result: 2 3/8 in.

2. Metric to fractional inches
   Translate 35 mm to a fractional inch (nearest 1/16).

$$\text{in} = \frac{35}{25.4} = 1.378\,\text{in}\ 0.378 \times 16 = 6.05 \Rightarrow 1\,\tfrac{6}{16} = 1\,\tfrac{3}{8}$$

Result: about 1 3/8 in (with metric reference 35 mm).

Tips and pitfalls

• Choose the smallest denominator that matches your tooling; cabinetry often stops at 1/16, precision machining may need 1/64.
• Decimal inches from CAD often include thousandths—round only after converting to avoid accumulating errors.
• When the rounded numerator equals the denominator (e.g., 7.999/8 rounds to 8/8), bump the whole-inch count by one and reset the fraction to 0.
• If you receive drawings in mm, convert everything to fractional inches before handing them to field crews to avoid mix-ups.

References and further reading

• NIST — Inch definition and exact conversion to metric
• Engineering Toolbox — Decimal inch to fraction table