How to Add Feet and Inches by Hand (Step by Step)

To add feet and inches, add the feet together, add the inches together, then carry any 12 inches over into one more foot. Fractions get a step of their own, and they are where most slips happen.

Step 1: Add each column separately

Take 4 ft 7 in plus 2 ft 8 in. Feet first: 4 + 2 = 6. Then inches: 7 + 8 = 15. You now have 6 ft 15 in, which is not finished yet.

Step 2: Carry every 12 inches

Twelve inches make one foot. Fifteen inches is one foot and three inches, so move the foot across: 6 ft + 1 ft = 7 ft, leaving 3 in. The answer is 7 ft 3 in.

Step 3: Add the fractions first

With fractions, work from the smallest part outward. Add 3 ft 5 3/8 in and 1 ft 9 5/8 in:

Fractions: 3/8 + 5/8 = 8/8, which is 1 whole inch.
Inches: 5 + 9 + 1 = 15, so carry 1 foot and keep 3 inches.
Feet: 3 + 1 + 1 = 5.

The answer is 5 ft 3 in.

When the denominators differ, convert to the smaller marks first. For example, 1/4 + 3/16 becomes 4/16 + 3/16 = 7/16. If you need a refresher on those marks, see how to read a tape measure.

Subtracting works the same way, in reverse

If the inches you are taking away are larger than the inches you have, borrow one foot and add 12 inches. For 5 ft 3 in minus 2 ft 8 in, borrow: 4 ft 15 in minus 2 ft 8 in is 2 ft 7 in.

Where hand arithmetic goes wrong

Forgetting to carry the 12 inches.
Adding fractions with different denominators without converting them.
Mixing decimal inches with fractions in the same sum.

Tape Mark does this for you. Enter feet, inches and fractions, and the app shows the exact result, a clearly labelled rounded measurement at the precision you choose, and where it falls on a drawn tape. It works offline, with no account and no ads. See the Tape Mark page for more.

Frequently asked questions

How many inches are in a foot?

Twelve. Convert any total over 11 inches into feet before you write the answer.

How do I add fractions with different bottoms?

Convert them to the same denominator, usually the smaller mark on your tape such as sixteenths, then add the tops.

Should I round before or after adding?

After. Rounding each piece first lets small errors pile up across a long run of cuts.