What is the Feet and Inches Arithmetic Calculator?
This tool adds, subtracts, multiplies, divides, scales, or converts lengths written in feet and inches. Each value can be a whole number, a decimal, a simple fraction, or a mixed number such as "61 3/4". Results appear as feet+inches with a tape-measure fraction, decimal feet, and decimal inches. It uses US-customary units (1 foot = 12 inches), but the arithmetic is universal.
How to use it
Enter the first length in the feet and inches boxes. Pick an operation. For two-length operations (add, subtract, multiply, divide) enter the second length. For "Multiply by factor" or "Divide by factor" enter a plain number in the factor box. Choose how finely to round the inch fraction (default 1/8"). Then read the answer in all formats.
The formula
Every value is normalized to decimal inches: $$\text{total} = \text{feet} \times 12 + \text{inches}$$. The chosen operation runs on those inch totals. The result R is converted back: whole \(\text{feet} = \left\lfloor R/12 \right\rfloor\); remaining inches are rounded to the nearest 1/denominator and reduced to lowest terms; a carry pushes 12 in up to 1 ft.
Worked example
First value: 0 ft, 61 3/4 in = \(61.75\) in. Add a second value of 21 ft 7 3/8 in = \(252 + 7.375 = 259.375\) in. $$R = 61.75 + 259.375 = 321.125 \text{ in} = 26.7604 \text{ ft} = 26 \text{ ft } 9\tfrac{1}{8} \text{ in} = 321\tfrac{1}{8} \text{ in}$$
FAQ
What does multiplying two lengths give? Length x length is technically an area; the calculator carries the raw numeric product through the same length formatting for convenience.
What about dividing two lengths? Length / length is a dimensionless ratio (a pure number), so it is shown as a single value.
Can results be negative? Yes. Subtraction can produce a negative length; the sign is shown and the magnitude is formatted normally.
