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Feet and Inches Calculator

Type two lengths the way you write them on a cut list, 5 ft 6 in, 5' 6", 5 6 1/2, 3 1/8" or a plain 66 inches, and add or subtract them, or multiply and divide one of them by a plain number. Every length is held as one whole number over another rather than as a decimal, so eighths and sixteenths add up cleanly and a third of an inch stays a third instead of becoming 0.33333 and drifting. The answer comes back in four forms at once: feet and inches, total inches, decimal feet and metres. Pick the fraction you actually cut to, 1/8, 1/16, 1/32 or none at all, and when the answer will not land on it the page prints the exact amount it moved, as a fraction, rather than absorbing it quietly. Nothing is uploaded and no account is needed; the only thing kept is your last two lengths and your rounding choice, in this browser.

5 ft 6 in + 2 ft 9 in8 ft 3 in99 in · 8.25 ft · 2.5146 m
exactnothing rounded away
Length A
Operation
Length B
Round to

Each length box takes any of 5 ft 6 in, 5' 6", 5 6 1/2, 3 1/8" or a plain number of inches like 66, and fractions are kept as fractions all the way through. Swap exchanges the two lengths. Multiply and divide replace the second box with a plain number. A decimal that does not stop is cut short and marked with an ellipsis rather than rounded, so every digit on screen is a real digit of the length.

The answer lands on 1/8 in exactly, so nothing was rounded away.

  • Feet and inchesthe answer as you would call it out
    8 ft 3 in
  • Total inchesthe same length, in inches
    99 in
  • Decimal feetfor a spreadsheet
    8.25 ft
  • Metresone inch is exactly 25.4 mm
    2.5146 m

Worked cases

Each one is computed by the same code that answers your own lengths, every time this page loads.

  • 5 ft 6 in + 2 ft 9 inlands on a whole inch
    8 ft 3 in
  • 7 ft 3 1/8 in − 2 ft 5 3/4 ineighths kept exact
    4 ft 9 3/8 in
  • 10 ft 1/3 in rounded to 1/8the rounding is shown
    10 ft 3/8 in, up by 1/24 in
Exact fractions, and it tells you when it rounds. Feet, inches and fractions are held as exact fractions rather than decimals, so eighths and sixteenths add and subtract without drift. When the answer will not land on the fraction you chose to round to, the exact difference is printed next to it. Feet, inches and the fraction are one whole number over another from the box to the screen, so 1/3 of an inch stays 1/3 until you ask for a fraction that cannot hold it, and then the move is printed rather than hidden. Metres are a converted convenience rather than the stored value, though the conversion itself is exact: an inch has been exactly 25.4 mm since 1959.

Common questions

How do I add feet and inches?
Put one length in each box and leave the operation on +. The page converts both to inches, adds them exactly, and converts back: 5 ft 6 in is 66 inches, 2 ft 9 in is 33 inches, and the 99 inches that come out are written as 8 ft 3 in. You never have to carry the twelve yourself, and you never have to turn the inches into a decimal first. Write each length however you like: 5 ft 6 in, 5' 6", 5 6, or 66 for plain inches all read as the same length.
How do I enter a fraction of an inch?
Write it after the whole inches, with a space: 3 1/8" is three and an eighth inches, and 7 ft 3 1/8 in is a full length. A fraction on its own works too, so 1/8 is an eighth of an inch. The fraction is kept as a fraction for the whole calculation, which is the point of this page: 7 ft 3 1/8 in minus 2 ft 5 3/4 in is exactly 4 ft 9 3/8 in here, with no decimal anywhere in the middle to lose the eighth. A glyph pasted from a document, as in 3 and a half inches written with the half symbol, reads the same as typing 3 1/2.
What happens when the subtraction goes below zero?
You get a negative length, written with one minus sign on the front: 2 ft minus 5 ft 6 in is -3 ft 6 in, which is -42 inches or -3.5 feet. Nothing is flipped around or turned into an absolute value, because the sign is usually the answer you wanted: it says the first length is short of the second by 3 ft 6 in. Rounding treats a negative length as the mirror of the positive one, so subtracting a length rounds the same way adding it did.
What does rounding to the nearest sixteenth do to the answer?
It moves the answer on to the closest sixteenth of an inch and then says how far it moved, and eighths and thirty seconds work the same way. Round 10 ft 1/3 in to the nearest eighth and you get 10 ft 3/8 in, up by 1/24 in: that 1/24 is the exact difference, printed as a fraction, and the exact value before rounding is listed underneath. When the answer already sits on the fraction you picked, the page says nothing was rounded away, because nothing was. Choose Exact and no rounding happens at all, so a third of an inch stays a third.
How do I convert the result to metres?
It is already there, on the line under the answer and in the results list. One inch has been exactly 25.4 millimetres since the 1959 international agreement, so the conversion is arithmetic on exact numbers rather than an approximation: 99 inches is 2.5146 m exactly. Where a length in metres has a decimal that never stops, the digits are cut short and marked with an ellipsis instead of being rounded, so every digit shown is a real digit of the length at that place.
Can I multiply a length by a number?
Yes. Choose the multiply or divide button and the second box becomes a plain number rather than a length: 5 ft 6 in times 3 is 16 ft 6 in, and 5 ft 6 in shared by 4 is 1 ft 4 1/2 in. Multiplying a length by a length would give an area, which is not what this page does, so a length typed into that box is refused with a message saying so rather than guessed at. Dividing by zero is refused too.
Does this calculator round the way a tape measure does?
Only when you ask it to. The rounding step is yours to pick: eighths, sixteenths, thirty seconds, or Exact for no rounding. Rounding goes to the nearest step, and a value sitting exactly half way goes away from zero, so 1/16 in rounds up to 1/8 in and -1/16 in rounds down to -1/8 in. Whatever the step, the exact answer is worked out first and the rounding is applied once at the end, so a long chain of eighths never accumulates a drift the way repeated decimal rounding does.

Feet, inches and fractions are held as exact fractions rather than decimals, so eighths and sixteenths add and subtract without drift. When the answer will not land on the fraction you chose to round to, the exact difference is printed next to it.