Feet and inches calculator
Add, subtract, multiply, and divide measurements in feet, inches, and fractions. Enter any notation — the calculator converts, works at full precision, and shows the arithmetic.
Your measurements
Three courses, two and a half lengths — a count, not a measurement.
21' 4-1/4"
A tape you can scroll back through, in the order you entered it, is in the app — along with memory registers and a keypad with ft, in and a/b on it.
total = a + b
Tape measure fractions, 1/16 to 1 inch
| Fraction | Inch | Foot | mm |
|---|---|---|---|
| 1/16 | 0.0625 | 0.005208 | 1.5875 |
| 1/8 | 0.125 | 0.010417 | 3.175 |
| 3/16 | 0.1875 | 0.015625 | 4.7625 |
| 1/4 | 0.25 | 0.020833 | 6.35 |
| 5/16 | 0.3125 | 0.026042 | 7.9375 |
| 3/8 | 0.375 | 0.031250 | 9.525 |
| 7/16 | 0.4375 | 0.036458 | 11.1125 |
| 1/2 | 0.5 | 0.041667 | 12.7 |
| 9/16 | 0.5625 | 0.046875 | 14.2875 |
| 5/8 | 0.625 | 0.052083 | 15.875 |
| 11/16 | 0.6875 | 0.057292 | 17.4625 |
| 3/4 | 0.75 | 0.062500 | 19.05 |
| 13/16 | 0.8125 | 0.067708 | 20.6375 |
| 7/8 | 0.875 | 0.072917 | 22.225 |
| 15/16 | 0.9375 | 0.078125 | 23.8125 |
| 1 | 1 | 0.083333 | 25.4 |
The four columns a drawing, a tape, a survey and a metric spec each want.
Feet, inches and fractions do not add the way decimals do. The usual mistake is to add the feet to the feet and the inches to the inches and hope the carry works out. This feet and inches calculator takes both measurements to a single length, works there, and gives the answer in feet-inches with the fraction, decimal feet, decimal inches, or millimetres.
How to add feet and inches
Convert both measurements to inches, add, then convert back: twelve inches to the foot going in, and twelve out again coming back. The carry is the part people drop. 8 ft 9 in plus 6 ft 5 in is 14 ft 14 in, which is 15 ft 2 in — and if the inches came with fractions, those need a common denominator before any of that happens.
Feet and inches to inches, and back
Multiply the feet by twelve and add the inches. 5 ft 7 in is 67 in. Going the other way, divide by twelve: the whole number is the feet and the remainder is the inches, so 100 in is 8 ft 4 in. Every answer above carries both forms at once.
Decimal feet vs inches — the common error
A decimal foot is not an inch. 5.7 ft is 5 ft 8-3/8 in, not 5 ft 7 in, and confusing the two is the commonest error on a site. Surveyors and civil drawings use decimal feet; carpenters use fractions. This calculator converts between them without either side rounding first.
Multiplying and dividing a measurement
Multiplying by a plain number scales a length: three courses of 7-3/16 in is 21-9/16 in. Dividing splits one: a 10 ft run into three equal parts is exactly 3 ft 4 in, but into seven parts it is not a figure any tape carries — so the answer comes back rounded to your chosen resolution and marked with ≈ to say it is not exact. Most calculators round that silently.
Sixteenths, thirty-seconds, and sixty-fourths
Set the resolution to the finest mark on your tape and every answer lands on a mark you can find. A framer works to a sixteenth; a cabinetmaker to a thirty-second or finer. The arithmetic runs at full precision the whole way through and rounds once, on the way to the screen, so a sixteenth added sixteen times is exactly one inch.
Questions about feet and inches
How do you add feet and inches?
Convert both measurements to inches, add them there, then convert back — twelve inches to the foot going in and twelve out again coming back. The carry is the part people drop: 8 ft 9 in plus 6 ft 5 in is 14 ft 14 in, which is 15 ft 2 in. If the inches carry fractions on top, those need a common denominator before any of it happens.
How do you convert feet and inches to inches?
Multiply the feet by twelve and add the inches. 5 ft 7 in is 67 in, and 12 ft 6-1/2 in is 150.5 in. The calculator shows the total inches for every answer, so the conversion never needs doing by hand.
How do you convert inches to feet and inches?
Divide by twelve. The whole number is the feet and the remainder is the inches, so 100 in is 8 ft 4 in and 256.25 in is 21 ft 4-1/4 in.
What is 5 feet 7 inches in decimal feet?
5.5833 ft. Seven inches is 7 ÷ 12 of a foot, which is 0.5833. Note that this is not 5.7 — a decimal foot is not an inch, and confusing the two is the commonest error on a drawing.
What is 1/16 of an inch as a decimal?
0.0625 in, which is 0.005208 ft or 1.5875 mm. The full table of sixteenths is above, with the decimal inch, the decimal foot and the millimetres for each one.
How do you multiply feet and inches?
Take the measurement to inches, multiply by the plain number, and convert back. Three courses of 7-3/16 in is 21-9/16 in, or 1 ft 9-9/16 in. Set the operator to × and the second field takes the number rather than a second measurement.
How do you divide a measurement into equal parts?
Set the operator to ÷ and enter how many parts. A 10 ft run split three ways is exactly 3 ft 4 in; split seven ways it is not a figure any tape carries, so the answer comes back rounded to your resolution and marked with ≈ rather than presented as exact.
Can Excel add feet and inches?
Not directly. Excel has no fraction type, so 12' 6-1/2" is either text it cannot add or 12.541666… it can. A custom number format will display feet and inches but it will not add them, which is why the formula people pass around for this is several nested functions long and still loses a sixteenth.