How to Convert mm to Fractional Inches

There are 25.4 millimeters in an inch.
••• measuring tool image by Michalis Palis from

Converting millimeters (mm) to fractional inches is a matter of rounding to the nearest 16th of an inch, since this is how far inches are broken down on rulers. The conversion factor between inches and mm is 25.4.

    Measure or identify the length in mm for the object of interest.

    Divide the amount in Step 1 by 25.4 to get the inches in decimal form.

    Take the decimal portion of the result of Step 2 and multiply it by 16. The point is to determine the nearest 16th of an inch on a ruler.

    For example, 120 mm divided by 25.4 yields 4.7244 inches. Multiplying the 0.7244 by 16 gives 11.591. Round this to 12/16, or 3/4. The result, therefore, is 4 3/4 inches.


    • If you’re making the conversion from mm to fractional inches for tools, you’ll probably want to use 32 instead of 16. Following the exact same calculations but using 32 instead of 16, the answer for the example would become 4 23/32 inches. Wire width conversion could entail converting to the nearest 64th of an inch.

Related Articles

How to Convert Decimal to Ruler Measurement
How to Convert Inches to the Metric System
How to Convert Inches to 16ths of an Inch
How to Calculate Height, Width & Square Feet
How to Calculate Paper Roll Length by Roll Diameter
How to Calculate a Circular Area
How to Find the Volume of a Sphere in Terms of Pi
How to Convert From Metric to Feet and Inches
How to Convert Centimeters to Meters
How to Calculate Circumference in Inches
How to Find Mass in Weight
How to Use a Protractor
How to Find The Slope of a Line Given Two Points
How to Subtract Feet & Inches
How to Convert 46 CM Into Inches
How to Calculate Area of an Obtuse Triangle
How to Convert 55 X 40 X 20 CM to Inches
How to Find the Circumference of an Octagon
How to Calculate a Temperature Range
How to Find the Area & Width of a Rectangle