A Fraction To Mm Calculator is a precision tool used to convert a measurement given in fractions of an inch into its equivalent value in millimeters. This conversion is essential in many technical fields, including engineering, manufacturing, and woodworking, where plans may use the imperial system (inches) but the tools or materials are specified in the metric system (millimeters). The calculator automates the two-step process of first turning the fraction into a decimal inch value and then multiplying it by the standard conversion factor. Consequently, it eliminates manual calculation errors and provides a quick, accurate conversion for seamless work between the two measurement systems.
formula of Fraction To Mm Calculator
To convert a fraction of an inch to millimeters, you first convert the fraction to a decimal, then multiply by the conversion factor of 25.4.
Decimal Inch Value × 25.4 = Value in mm
Where:
Decimal Inch Value = The fraction expressed as a decimal (e.g., for 1/4, the decimal value is 0.25). You find this by dividing the numerator by the denominator.
25.4 = The exact number of millimeters in one inch.
Common Inch Fraction to Millimeter Conversion Chart
This table provides a quick reference for the millimeter equivalents of common fractions of an inch. It is especially useful for quickly identifying standard drill bit or fastener sizes.
| Fraction of an Inch | Decimal Equivalent | Millimeter (mm) Value |
| 1/16" | 0.0625 | 1.5875 mm |
| 1/8" | 0.125 | 3.175 mm |
| 1/4" | 0.25 | 6.35 mm |
| 3/8" | 0.375 | 9.525 mm |
| 1/2" | 0.5 | 12.7 mm |
| 5/8" | 0.625 | 15.875 mm |
| 3/4" | 0.75 | 19.05 mm |
| 7/8" | 0.875 | 22.225 mm |
| 1" | 1.0 | 25.4 mm |
Example of Fraction To Mm Calculator
Let's calculate the millimeter equivalent of the measurement 3/8 of an inch.
Step 1: Convert the fraction to a decimal.
To do this, you divide the numerator by the denominator.
3 ÷ 8 = 0.375
So, 3/8 of an inch is equal to 0.375 inches.
Step 2: Multiply the decimal value by the conversion factor.
Value in mm = Decimal Inch Value × 25.4
Value in mm = 0.375 × 25.4 = 9.525 mm
Therefore, 3/8 of an inch is exactly equal to 9.525 millimeters.
Most Common FAQs
The value of 25.4 is the internationally agreed-upon standard for the conversion between inches and millimeters, established in 1959. This definition ensures that measurements are consistent and precise across all countries and industries that use both the imperial and metric systems.
To convert a mixed number, you handle the whole number and the fraction separately and then add the results. First, convert the whole inches to millimeters (2 × 25.4 = 50.8 mm). Next, convert the fraction to millimeters (1/4" = 6.35 mm). Finally, add the two values together: 50.8 mm + 6.35 mm = 57.15 mm.
Yes, this is one of its most common and practical uses. Many tools, such as drill bits, wrenches, and sockets, are sold in both fractional inch sizes and metric millimeter sizes. This calculator allows you to quickly find the closest metric equivalent to an imperial size, which is very helpful when a specific size is not available in one system.