Dimensional math
Use ' for feet and " for inches, with a space before a fraction. The answer updates as you type. Click an example to try it.
- add two lengths
- subtract
- split into equal parts
- repeat a length
- area in square feet
- a slab in cubic yards
- parentheses work
- mix in metric
5ft 3in,5 feet 3 inchesand5' 3all mean five feet three inches.5'-3 1/2"written tight, the way drawings show it, is a single dimension. With spaces —5' - 3 1/2"— it subtracts.- Decimals work anywhere:
2.5'is 2' 6". So domm,cm,mandyd. - Two lengths multiplied give square feet, three give cubic feet and cubic yards, and a length divided by a length gives a count.
- Press M+ beside a result to add it to a running total, which is handy for cut lists.
Questions
How do I add feet and inches?
Add the feet together and the inches together, then carry: every 12 inches becomes 1 foot. For example 5' 9" + 3' 8" is 8' 17", which is 9' 5". In the calculator, type 5' 9" + 3' 8".
How do I type a fraction of an inch?
Put a space between the whole inches and the fraction: 7' 9 1/2" is seven feet, nine and a half inches. A hyphen works too, as in 9-1/2".
Can I multiply feet by feet?
Yes. Two lengths multiplied give an area in square feet, and three give a volume in cubic feet and cubic yards. For example 12' x 10' is 120 sq ft.
How precise is the answer?
The math is done at full precision and only the displayed fraction is rounded, to the nearest 1/16 inch by default. You can change that from 1/2 down to 1/64. When rounding changes the value, the answer is marked with ≈.
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