Fraction to decimal inches
This reads and rounds the number you type — nothing more. The fraction is snapped to the nearest tape mark, so on a precision setup work from the decimal instead. Measure against the actual part before you cut.
Type a fraction, a whole-and-fraction, or a feet-inches dimension and the decimal appears at once. Type a decimal in the second box and it comes back as the nearest sixteenth and thirty-second — the two marks you are most likely to be cutting to.
Worked example
A cut list reads 2 5/16″. That is 2 + 5 ÷ 16 = 2.3125 in. Now suppose a CNC setup gives you 2.28 inch and you need a tape mark: to the nearest sixteenth that is 2 5/16″, and to the nearest thirty-second 2 9/32″.
The formula
decimal = whole + numerator ÷ denominator
A fraction is just a division waiting to happen, and feet add twelve inches apiece. Going back the other way, the decimal is multiplied by 16 (or 32), rounded to a whole number of ticks, and reduced — which is exactly how a tape's markings are laid out.
Questions
- How do I turn a fraction of an inch into a decimal?
- Divide the top of the fraction by the bottom. So 3/8 is 3 ÷ 8 = 0.375, and 2 5/16 is 2 + 5 ÷ 16 = 2.3125. This tool reads whole-and-fraction and feet-inches shapes as well, so you can type what is written on the drawing and get the decimal straight back.
- How do I go from a decimal back to a tape fraction?
- Type the decimal in the second box and the tool snaps it to the nearest sixteenth and thirty-second, the marks a tape actually carries. A reading of 0.4 inch, for instance, comes out as 3/8 to the sixteenth — the nearest line you can cut to.
- What input shapes does it understand?
- Bare inches like 7, fractions like 5/8, whole-and-fraction like 3 5/8, and feet-inches like 12′ 3 5/8″ or 12′-3-5/8. A dash inside the inches is treated as a separator, not a minus, which is how framing dimensions are usually scribbled.
- Why round to sixteenths and thirty-seconds?
- Because that is what the tool in your hand is graduated in. A decimal like 0.418 inch means nothing at the saw; 7/16 does. The exact decimal stays on screen for setups that read thousandths, but the fraction is what you mark and cut.
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