Feet and Inches Calculator

How to add feet and inches

Add the feet and the inches separately, then carry every 12 inches into a foot:

The answer is 9′ 5 1/8″, or 113 1/8 inches. To add the fractions, bring them to the same bottom number: 3/8 + 3/4 is 3/8 + 6/8 = 9/8, which is 1 1/8. The calculator does the same thing by turning each length into inches, adding, and converting back to feet, inches and the nearest fraction. Add as many rows as you need — the trim pieces around a room, the treads of a staircase — and each row shows the running total.

Subtracting feet and inches

When the inches you take away are larger than the inches you have, borrow one foot as 12 inches. For 12′ 6″ − 4′ 8 1/2″, write 12′ 6″ as 11′ 18″; then 18 − 8 1/2 is 9 1/2 and 11 − 4 is 7, giving 7′ 9 1/2″. In the calculator, tap the + next to a row to turn it into −. Subtracting is how you find a gap — the space left for a cabinet, or how much of a board is left after a cut.

Multiplying and dividing lengths

Choose × by to repeat a length — 7′ 3 5/16″ four times for four shelves — or ÷ by to split it into equal parts. Ten feet divided by 3 is exactly 3′ 4″; divided by 7 it is 17.1429 inches, which rounds to 1′ 5 1/8″.

For real cuts, remember the saw kerf: each cut turns about 1/8″ of wood into sawdust. Cutting an 8-foot (96″) board into 3 equal pieces takes 2 cuts, so the pieces are (96 − 2 × 1/8) ÷ 3 = 31.917″, or 31 15/16″ — not 32″. Subtract the kerf as a row before dividing: 96 minus 1/4, then ÷ 3. For the lumber volume of the pieces, use the board foot calculator.

Reading fractions on a tape measure

Most tape measures mark sixteenths of an inch: the longest line between inch numbers is 1/2, then 1/4, 1/8 and the shortest 1/16. That is why the calculator rounds to the nearest 1/16″ by default and shows how much the rounding changed the length. Woodworkers and machinists working to 1/32″ or 1/64″ can change the precision; framers and drywall installers often round to 1/8″. To work with fractions on their own — adding 5/8 and 7/16, say — use the fraction calculator.

Feet, inches and metric

An inch is exactly 2.54 centimeters, so a foot is 30.48 cm and 9′ 5 1/8″ is 287.34 cm. Plans from other countries, flooring sold in meters and European hardware all mix into the same list: type 2 m, 30 cm or 600 mm in a row and the calculator converts it before adding. The result shows the total in centimeters and meters as well as decimal feet and yards. For single conversions, see inches to feet and inches to cm; for the area of a floor or wall from lengths in feet and inches, the square footage calculator.