Feet and inches calculator
Add, subtract, multiply, and divide feet-inch-fraction measurements the way a tape reads them, with the answer rounded to the nearest sixteenth. Same math the CutOnce app runs, where this calculator is free forever.
Updated
Type the way your tape reads: 5 ft 6-1/2 in, 66.5, or 5′ 6-1/2″. Multiply and divide take a plain number.
- Result
- 8 ft 2-1/4 in
How to add feet and inches
To add feet and inches, add the fractions, then the inches, then the feet, and carry every 12 inches up to the next foot. So 5 ft 6-1/2 in plus 2 ft 7-3/4 in is 14-1/4 in of inches, which is 1 ft 2-1/4 in, giving 8 ft 2-1/4 in. The calculator above does the carrying and the fraction work for you and rounds to the nearest sixteenth.
A worked example
Two tape readings added. The result is computed by the same function that drives the calculator above.
| First measurement | 5 ft 6-1/2 in |
| Second measurement | 2 ft 7-3/4 in |
| Sum | 8 ft 2-1/4 in |
How the tape math works
- 01
Line up the fractions
Inch fractions on a tape are sixteenths, eighths, quarters, and halves, all powers of two, so they share a denominator. 1/2 is 8/16, 3/4 is 12/16, and 8/16 plus 12/16 is 20/16, which is 1-4/16, or 1-1/4 in.
- 02
Carry the inches into feet
Add the whole inches and any carry from the fractions, then roll every 12 inches into a foot. Fourteen and a quarter inches becomes 1 ft 2-1/4 in. This is the step a decimal calculator skips and a tape does not.
- 03
Round to the tape
The app keeps every value to the sixty-fourth internally, then shows it to the nearest sixteenth, because that is the finest mark on most tapes. You get a number you can actually pull, not 8.1875 ft.
Common questions
- How do you add feet and inches on a calculator?
- A plain calculator makes you convert everything to inches or to decimal feet first, add, then convert back. This one takes the tape reading directly, so you type 5 ft 6-1/2 in and 2 ft 7-3/4 in and read 8 ft 2-1/4 in with no conversion.
- What is 1/2 plus 3/4 of an inch?
- 1-1/4 in. As sixteenths that is 8/16 plus 12/16, which is 20/16, and 20/16 is 1 and 4/16, or 1-1/4 in. The calculator carries that extra inch for you.
- Can it multiply a measurement, like for a stud count?
- Yes. Set the operation to multiply and the second field takes a plain number: 16-1/4 in times 12 studs is 16 ft 3 in. Divide works the same way for splitting a length into equal pieces.
- Why round to a sixteenth?
- Because that is the smallest mark on a standard tape, so it is the smallest cut you can lay out by eye. The app holds finer precision while it works and only rounds for the answer, so rounding does not pile up across a run.
This one is free, forever
The feet-inch-fraction calculator is free forever in the CutOnce app, with a running tape that keeps 500 calculations and exports to PDF. The one-time purchase unlocks the rest of the toolbox.
See also