Enter any mm value and instantly see the nearest fractional inch at every precision level — from halves to sixty-fourths.
Need to convert metric millimeter measurements into standard fractional inches for machining, woodworking, or engineering?
While the metric system relies on clean decimals, the Imperial system frequently uses fractions like 1/2″, 1/4″, or 1/16″. This page provides a quick-reference guide, step-by-step mathematical formulas, a complete mm to fractional inches chart, and dedicated breakdowns for common sizes like 2mm, 6mm, 8mm, and 10mm.
This master reference chart covers all common millimeter sizes, providing the exact decimal inch conversion and the closest fractional equivalents down to 1/64″ precision.
| Millimeters (mm) | Decimal Inches (in) | Nearest 1/16″ | Nearest 1/32″ | Nearest 1/64″ |
| 1 mm | 0.0394″ | 0″ | 3/64″ | 3/64″ |
| 2 mm | 0.0787″ | 1/16″ | 5/32″ | 5/64″ |
| 3 mm | 0.1181″ | 1/8″ | 1/8″ | 1/8″ (Approx) |
| 4 mm | 0.1575″ | 3/16″ | 5/32″ | 5/32″ |
| 5 mm | 0.1969″ | 3/16″ | 3/16″ | 13/64″ |
| 6 mm | 0.2362″ | 1/4″ | 1/4″ | 15/64″ |
| 7 mm | 0.2756″ | 1/4″ | 9/32″ | 9/32″ |
| 8 mm | 0.3150″ | 5/16″ | 5/16″ | 5/16″ |
| 9 mm | 0.3543″ | 3/8″ | 11/32″ | 23/64″ |
| 10 mm | 0.3937″ | 3/8″ | 13/32″ | 25/64″ |
| 12 mm | 0.4724″ | 1/2″ | 15/32″ | 15/32″ |
| 14 mm | 0.5512″ | 9/16″ | 9/16″ | 35/64″ |
| 16 mm | 0.6299″ | 5/8″ | 5/8″ | 5/8″ |
| 18 mm | 0.7087″ | 11/16″ | 23/32″ | 45/64″ |
| 20 mm | 0.7874″ | 13/16″ | 25/32″ | 25/32″ |
If you need to handle the calculations behind the scenes without an online utility, you can follow these core conversion steps.
By international agreement, 1 inch is exactly equal to 25.4 millimeters. To find the decimal inch value, divide your millimeter measurement by 25.4.
Formula: Inches (Decimal) = Millimeters / 25.4
To convert that decimal value into a physical fraction of an inch (using standard denominators like 16, 32, or 64):
Formula: Numerator (Rounded) = Round(Inches (Decimal) x Denominator)
If you need to go backward from an Imperial fraction to a clean decimal, simply divide the top number (numerator) by the bottom number (denominator):
Formula: Decimal = Numerator / Denominator
Example: For 3/8″, calculate 3 / 8 = 0.375″.
2mm is closest to 5/64″ when utilizing high precision, or 1/16″ for quick, rough measurements.
6mm is closest to 15/64″. For general hardware and workshop applications, it is incredibly close to a standard 1/4″ fraction.
Not exactly, but they are very close. A 3/8″ wrench equals 9.525mm, meaning a 10mm bolt head is slightly too large for a 3/8″ tool. 10mm is precisely closest to 25/64″.
In 1959, the international yard and pound agreement standardized the inch to be exactly equal to 25.4 millimeters, making it the universal constant for all metric-to-imperial conversions.
Rough carpentry, framing lumber, concrete formwork. Acceptable when visual fit matters more than fit precision.
General woodworking, shelving, cabinetry. Standard for most non-structural cuts.
Finish carpentry, furniture, most hardware. Industry standard for woodworking joints.
Precision woodwork, metal fabrication, machined surfaces. Most rulers show 1/16".
Sheet metal, precision machining, close-fit assemblies. Standard machinist ruler.
Fine instrument work, gauge blocks, precision engineering. Smallest common US fraction.
| Fraction | Decimal Inches | Millimeters | Centimeters |
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