Convert MM to inches (decimal & fractional), cm, feet, meters, and more. Includes drill bit chart and fractional inch reference.
The MM (millimeters) conversion calculator provides comprehensive conversion from millimeters to all common length units, with a special focus on the mm-to-inch relationship that engineers and craftspeople use daily. Unlike basic converters, this tool shows both decimal and fractional inch equivalents (to the nearest 1/32"), making it ideal for woodworking, metalworking, and machining.
Millimeters are the standard unit in metric engineering drawings, while inches (often as fractions) dominate in US manufacturing and construction. This converter bridges both worlds with instant, bidirectional conversion and practical reference tables.
The built-in drill bit size chart maps standard number, letter, and fractional drill sizes to their mm equivalents, and the quick reference table highlights your current value for easy comparison. Configure decimal precision from 0 to 12 places depending on your application. It is particularly helpful when purchasing tools, validating part dimensions, and cross-checking supplier specifications before fabrication. It also supports faster handoff between design teams, machinists, and installers who prefer different measurement conventions.
Working with both metric and imperial measurements is a daily reality in manufacturing, construction, and international trade. This mm converter eliminates the need for separate conversion charts and drill bit references by combining everything into one interactive tool with instant bidirectional conversion. It reduces setup time on the shop floor and improves confidence when tolerances are tight or material waste is costly.
MM Conversion: 1 inch = 25.4 mm (exact). 1 cm = 10 mm. 1 m = 1000 mm. 1 ft = 304.8 mm. Fractional inches: round to nearest 1/32" by computing (mm ÷ 25.4) × 32, rounding, then reducing the fraction.
Result: 0.25 inches = 1/4"
6.35 mm ÷ 25.4 = 0.25 inches exactly. As a fraction, 0.25 = 1/4 inch. This is the diameter of a standard 1/4" drill bit.
Millimeters provide the ideal granularity for workshop measurements. A 0.1mm caliper reading is meaningful and actionable, whereas the imperial equivalent (0.004") requires mental conversion. Modern CNC machines, 3D printers, and laser cutters all default to millimeters. When receiving metric-dimensioned parts or plans from international suppliers, knowing how to read and convert mm measurements is essential.
The US trades traditionally use fractional inches: 1/2", 1/4", 1/8", 1/16", 1/32", and sometimes 1/64". Each fraction represents a specific mm value: 1/2" = 12.7mm, 1/4" = 6.35mm, 1/8" = 3.175mm. Tape measures and rulers show these fractions, but shop drawings may use either decimal or fractional notation. Being fluent in both systems prevents costly cutting errors.
Beyond direct measurement, many industries use gauge or number systems that map to specific mm dimensions. Sheet metal gauge (e.g., 14ga = 1.98mm), wire gauge (AWG 12 = 2.053mm diameter), and screw sizes (M6 = 6mm shaft) all require mm knowledge. This calculator serves as a central reference for all these mm-to-inch conversions in one place.
Divide mm by 25.4 to get decimal inches, then convert to the nearest fraction. For 1/32" precision: multiply decimal inches by 32, round to nearest whole number, and put over 32. Reduce the fraction. Example: 10mm = 0.3937" × 32 = 12.6 ≈ 13/32".
10mm equals 0.3937 inches, which is approximately 25/64" or close to 13/32". For practical purposes in woodworking, 10mm is just under 3/8" (9.525mm).
This calculator rounds to the nearest 1/32 of an inch (0.794mm precision). For most woodworking and construction, 1/16" precision suffices. For precision machining, use the decimal inch value instead of fractions.
This calculator adds fractional inch display, a drill bit size chart, and is optimized for shop/manufacturing use cases. The millimeter converter focuses on pure metric-imperial conversion with more unit options.
Number drill bits (#1-#80) decrease in size as the number increases. #1 = 5.791mm, #80 = 0.343mm. Letter drills (A-Z) are larger: A = 5.944mm, Z = 10.490mm. Fractional drill bits match their inch designation exactly.
In manufacturing, tolerances down to 0.01mm (10 µm) are common for precision parts. CNC machines can achieve 0.005mm accuracy. In everyday use, 0.5mm (half a millimeter, about the width of a mechanical pencil lead) is the practical limit.