Why add feet and inches by hand is error-prone
Feet and inches are a base-12 system, so ordinary column arithmetic does not work: 10 inches plus 8 inches is not 18, it is 1 foot 6 inches. When you add several lengths, it is easy to forget the carry or to borrow the wrong number when subtracting. The calculator converts everything to inches, does the arithmetic once and converts back.
It is also useful for body measurements and heights. A tape measure reads in inches and sixteenths, so the answer is rounded to the same precision.
Worked examples
5′ 10″ + 3′ 8″: 70 + 44 = 114 inches = 9′ 6″, which is 289.56 cm. 6′ 2″ − 3′ 9″: 74 − 45 = 29 inches = 2′ 5″, or 73.66 cm. 5′ 11¾″ + ½″ = 72¼ inches = 6′ ¼″.
Real-world uses
Builders add up wall lengths, lumber cuts and room dimensions, sewers add seam allowances, and anyone measuring furniture for a doorway or a room needs totals. If you need an area rather than a length, use the tile calculator or the paint calculator, and the unit converter handles other conversions between metric and imperial.
Questions people ask
How do you add feet and inches?
Add the feet together and the inches together, then carry: every 12 inches becomes 1 foot. For 5 ft 10 in + 3 ft 8 in, the feet add to 8 and the inches to 18, which is 1 ft 6 in, so the total is 9 ft 6 in.
How do you subtract feet and inches?
Convert both lengths to inches, subtract, and then convert back. For 6 ft 2 in − 3 ft 9 in that is 74 − 45 = 29 inches, which is 2 ft 5 in. If the second length is bigger, the answer is negative.
Can I use fractions of an inch?
Enter inches as decimals: 3½ is 3.5, ¼ is 0.25 and ⅛ is 0.125. The answer is shown rounded to the nearest sixteenth of an inch, as on a tape measure, while the total inches below show the exact value.
How many inches are in a foot?
There are 12 inches in a foot. A yard is 3 feet or 36 inches. One inch is exactly 2.54 centimetres or 25.4 millimetres, so 5 ft 10 in is 177.8 cm.
Why does the answer show a minus sign?
When you subtract a longer length from a shorter one the result is below zero. For 3 ft − 4 ft 6 in the answer is −1 ft 6 in, which just means the second length is 18 inches longer than the first.