mm to inches fraction
Convert millimeters to fractional inches with precision control for 1/16", 1/32", and 1/64" denominators. Our fraction converter provides accurate approximations with error calculations, essential for woodworking, metalworking, and precision manufacturing where imperial fractional measurements are standard practice. Understanding fractional inch notation is crucial when working with American tools, reading technical drawings, or following construction blueprints that specify measurements in fractions rather than decimal format. This millimeter-to-fraction calculator simplifies the conversion process while maintaining measurement accuracy.
Convert millimeters to fractional inches with precision control for 1/16", 1/32", and 1/64" denominators.
mm to inches fraction converter
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mm to inches fraction: conversion and rounding explained
The Rounding Process
Converting millimeters to fractional inches involves two steps: first converting metric millimeters to decimal inches using the standard factor (25.4mm = 1 inch), then rounding the decimal result to the nearest fraction based on your selected denominator. Since most millimeter measurements don't correspond to exact fractional inch values, this approximation process is necessary for practical use with standard measuring tools and imperial hardware specifications.
numerator = round(decimal_inches × denominator)
Example: 10mm = 0.3937" ≈ 25/64" (with 1/64 precision)
Choosing the Right Fraction Precision for Your Project
- 1/16" (0.0625")- Suitable for general carpentry, construction framing, basic woodworking projects, and rough measurements where high precision isn't critical. Most standard tape measures show sixteenths markings.
- 1/32" (0.03125")- Recommended for finish carpentry, cabinet making, precision metalworking, and mechanical fitting. Provides better accuracy for tight tolerances while remaining readable on quality measuring tools.
- 1/64" (0.015625")- Required for machining operations, engineering applications, precision instrument work, and when converting technical specifications from metric to imperial systems with minimal error tolerance.
Understanding Approximation Error in Fraction Conversion
The displayed approximation error represents the difference between the exact decimal inch value and the fractional approximation. For instance, 10 millimeters equals exactly 0.3937 inches, but rounds to 25/64" (0.390625"), producing an error of ±0.003075 inches. Higher denominators like 64ths yield smaller errors but create more complex fractions. When precision matters for your measurement application, selecting finer denominator increments reduces conversion error and improves dimensional accuracy in your final product or assembly.
Fractional MM to Inches Chart
Complete reference showing common fractional inch measurements from 1/64" to 1/2" with their precise decimal inch and millimeter equivalents. This bidirectional conversion table helps when working between metric and imperial systems, verifying fraction-to-decimal calculations, or identifying the closest fractional inch match for a given millimeter measurement. Essential reference for machinists, engineers, and craftspeople working with mixed measurement standards.
| Fraction | Millimeters | Decimal (in) |
|---|---|---|
| 1/64" | 0.397 | 0.015625 |
| 1/32" | 0.794 | 0.03125 |
| 3/64" | 1.191 | 0.046875 |
| 1/16" | 1.588 | 0.0625 |
| 5/64" | 1.984 | 0.078125 |
| 3/32" | 2.381 | 0.09375 |
| 7/64" | 2.778 | 0.109375 |
| 1/8" | 3.175 | 0.125 |
| 9/64" | 3.572 | 0.140625 |
| 5/32" | 3.969 | 0.15625 |
| 11/64" | 4.366 | 0.171875 |
| 3/16" | 4.763 | 0.1875 |
| 13/64" | 5.159 | 0.203125 |
| 7/32" | 5.556 | 0.21875 |
| 15/64" | 5.953 | 0.234375 |
| 1/4" | 6.35 | 0.25 |
| 17/64" | 6.747 | 0.265625 |
| 9/32" | 7.144 | 0.28125 |
| 19/64" | 7.541 | 0.296875 |
| 5/16" | 7.938 | 0.3125 |
| 21/64" | 8.334 | 0.328125 |
| 11/32" | 8.731 | 0.34375 |
| 23/64" | 9.128 | 0.359375 |
| 3/8" | 9.525 | 0.375 |
| 25/64" | 9.922 | 0.390625 |
| 13/32" | 10.319 | 0.40625 |
| 27/64" | 10.716 | 0.421875 |
| 7/16" | 11.113 | 0.4375 |
| 29/64" | 11.509 | 0.453125 |
| 15/32" | 11.906 | 0.46875 |
| 31/64" | 12.303 | 0.484375 |
| 1/2" | 12.7 | 0.5 |