Convert tape measure inch fractions (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4) to decimal inches, feet + inches, millimeters and centimeters with selectable precision.
Type inch fractions as 3 1/2, 7/16 or 15 3/8. Decimals work too: 15.875. For mm/cm, just enter a number.
Formula & how it works
Input is normalized to decimal inches (1 inch = 25.4 mm exactly). The fraction output rounds to the nearest step of 1/denominator and reduces to lowest terms. Feet + inches splits the integer foot count first, then shows the remainder as a fraction.
Tape measure reference table
| Fraction (in) | Decimal (in) | mm | cm |
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Frequently asked questions
How do tape measure fractions work?
Imperial tape measures divide each inch into binary fractions: halves, quarters, eighths, sixteenths and sometimes thirty-seconds. The longest mark after the inch is 1/2, the next-longest are 1/4 and 3/4, then 1/8 marks, then 1/16 marks. Converting to a fraction simply rounds your value to the nearest 1/16 (or chosen precision).
How do I convert a fraction like 3 1/2" to millimeters?
First convert the fraction to decimal: 3 1/2 = 3.5. Then multiply by 25.4 mm/in: 3.5 × 25.4 = 88.9 mm. The calculator above does this automatically and also shows centimeters, feet + inches and the nearest tape-measure fraction.
Why does 1/16" equal 1.5875 mm exactly?
Because 1 inch is defined as exactly 25.4 mm. So 1/16 inch = 25.4 / 16 = 1.5875 mm. Similarly 1/32" = 0.79375 mm and 1/64" = 0.396875 mm. These are exact rational numbers, not approximations.
What precision should I pick?
Framing carpentry: 1/16" is standard. Cabinet making and trim: 1/32". Machining and metalwork: 1/64" or switch to decimal inches or mm. For most DIY and construction tasks, 1/16" is enough — finer precision than a typical tape measure can read.
How do I convert mm back to an inch fraction?
Divide by 25.4 to get decimal inches, then round to the nearest step of 1/precision. Example: 100 mm ÷ 25.4 ≈ 3.9370", which rounds to 3 15/16" at 1/16 precision.
Does the calculator reduce fractions?
Yes. After rounding, the numerator and denominator are divided by their greatest common divisor, so 8/16 becomes 1/2 and 4/8 becomes 1/2. Whole inches and zero fractions are shown cleanly (e.g. 2", not 2 0/16").
This fractional inches converter accepts inch fractions in tape-measure notation, decimal inches, millimeters or centimeters and returns every common format at once. Type values like 3 1/2, 7/16 or 15.875, or enter a metric number to see the nearest tape-measure fraction at your chosen precision (1/2 through 1/64). Since 1 inch is defined as exactly 25.4 mm, every conversion is exact — for example 1/16 inch equals exactly 1.5875 mm. Results include the reduced fraction, decimal inches, feet + inches, millimeters and centimeters, plus a visual SVG tape with the marker placed on your value. The reference table lists all sixteenths from 1/16 up to 12 inches.