Feet and Inches Calculator
To add feet and inches, add the fractions and inches first and carry every 12 inches into a foot: 5' 7 3/8" + 2' 9 1/2" = 8' 4 7/8" (100.875 in, 8.40625 ft, 2,562.225 mm). Type lengths the way the tape reads, such as 5' 7 3/8", 5ft 7-3/8in, 67.375 in or 170 cm; the calculator works in exact fractions, rounds the answer to the nearest 1/16 inch (or 1/2 to 1/64), shows how far that is from the exact length, and marks it on a tape.
Updated Runs in your browser: nothing you enter is uploadedHow this tool works
5' 7 3/8" + 2' 9 1/2" = 8' 4 7/8"
8' 4 7/8"
Exact: no rounding at 1/16 inch.
- Feet and inches (to 1/16″)
- 8' 4 7/8"
- Inches (to 1/16″)
- 100 7/8"
- Decimal inches
- 100.875 in
- Decimal feet
- 8.40625 ft
- Millimeters
- 2,562.225 mm
- Centimeters
- 256.2225 cm
- Meters
- 2.562225 m
How to read a tape measure: the 1/16 marks in an inch
| Marks past the inch line | Fraction | Decimal inch | Millimeters | Which mark |
|---|---|---|---|---|
| 1 | 1/16" | 0.0625 | 1.5875 | 1/16 mark (shortest) |
| 2 | 1/8" | 0.125 | 3.175 | 1/8 mark |
| 3 | 3/16" | 0.1875 | 4.7625 | 1/16 mark (shortest) |
| 4 | 1/4" | 0.25 | 6.35 | 1/4 mark |
| 5 | 5/16" | 0.3125 | 7.9375 | 1/16 mark (shortest) |
| 6 | 3/8" | 0.375 | 9.525 | 1/8 mark |
| 7 | 7/16" | 0.4375 | 11.1125 | 1/16 mark (shortest) |
| 8 | 1/2" | 0.5 | 12.7 | 1/2 mark (second longest) |
| 9 | 9/16" | 0.5625 | 14.2875 | 1/16 mark (shortest) |
| 10 | 5/8" | 0.625 | 15.875 | 1/8 mark |
| 11 | 11/16" | 0.6875 | 17.4625 | 1/16 mark (shortest) |
| 12 | 3/4" | 0.75 | 19.05 | 1/4 mark |
| 13 | 13/16" | 0.8125 | 20.6375 | 1/16 mark (shortest) |
| 14 | 7/8" | 0.875 | 22.225 | 1/8 mark |
| 15 | 15/16" | 0.9375 | 23.8125 | 1/16 mark (shortest) |
| 16 | 1 inch | 1 | 25.4 | The next inch line (longest) |
Inches as decimal feet
| Inches | Decimal feet | Millimeters |
|---|---|---|
| 0" | 0 ft | 0 mm |
| 1" | ≈ 0.0833 ft | 25.4 mm |
| 2" | ≈ 0.1667 ft | 50.8 mm |
| 3" | 0.25 ft | 76.2 mm |
| 4" | ≈ 0.3333 ft | 101.6 mm |
| 5" | ≈ 0.4167 ft | 127 mm |
| 6" | 0.5 ft | 152.4 mm |
| 7" | ≈ 0.5833 ft | 177.8 mm |
| 8" | ≈ 0.6667 ft | 203.2 mm |
| 9" | 0.75 ft | 228.6 mm |
| 10" | ≈ 0.8333 ft | 254 mm |
| 11" | ≈ 0.9167 ft | 279.4 mm |
Common lengths in feet, inches and metric
| Length | Feet and inches | Decimal inches | Decimal feet | Millimeters |
|---|---|---|---|---|
| 1/16" | 1/16" | 0.0625 in | ≈ 0.0052 ft | 1.5875 mm |
| 1/8" | 1/8" | 0.125 in | ≈ 0.0104 ft | 3.175 mm |
| 1/4" | 1/4" | 0.25 in | ≈ 0.0208 ft | 6.35 mm |
| 3/8" | 3/8" | 0.375 in | 0.03125 ft | 9.525 mm |
| 1/2" | 1/2" | 0.5 in | ≈ 0.0417 ft | 12.7 mm |
| 5/8" | 5/8" | 0.625 in | ≈ 0.0521 ft | 15.875 mm |
| 3/4" | 3/4" | 0.75 in | 0.0625 ft | 19.05 mm |
| 1" | 1" | 1 in | ≈ 0.0833 ft | 25.4 mm |
| 6" | 6" | 6 in | 0.5 ft | 152.4 mm |
| 1' | 1' 0" | 12 in | 1 ft | 304.8 mm |
| 16" | 1' 4" | 16 in | ≈ 1.3333 ft | 406.4 mm |
| 2' 6" | 2' 6" | 30 in | 2.5 ft | 762 mm |
| 8' | 8' 0" | 96 in | 8 ft | 2,438.4 mm |
| 1 cm | 3/8" | ≈ 0.3937 in | ≈ 0.0328 ft | 10 mm |
| 10 cm | 3 15/16" | ≈ 3.937 in | ≈ 0.3281 ft | 100 mm |
| 1 m | 3' 3 3/8" | ≈ 39.3701 in | ≈ 3.2808 ft | 1,000 mm |
| 2 m | 6' 6 3/4" | ≈ 78.7402 in | ≈ 6.5617 ft | 2,000 mm |
How to add and subtract feet and inches by hand
- Line up the parts. Write both lengths as feet, whole inches and a fraction, one under the other: 5' 7 3/8" and 2' 9 1/2".
- Add the fractions. Give them a common bottom number and add: 3/8 + 1/2 = 3/8 + 4/8 = 7/8. If the sum is 1 or more, carry a whole inch.
- Add the inches and carry to feet. 7 + 9 = 16 inches, which is 1 foot 4 inches. Every 12 inches carry one foot.
- Add the feet. 5 + 2 + 1 carried = 8 feet, so the total is 8' 4 7/8".
- To subtract, borrow. When the top inches or fraction are smaller, borrow a foot as 12 inches (or an inch as 16/16): 12' 7 3/8" − 3' 10 5/8" = 8' 8 3/4".
Frequently asked questions
- How do I convert decimal feet to feet and inches?
- Keep the whole feet and multiply the decimal part by 12 to get inches. 8.40625 ft is 8 feet and 0.40625 × 12 = 4.875 inches, and 0.875 inch is 7/8, so it is 8' 4 7/8". To get the fraction, multiply the leftover decimal by 16 and round: 0.875 × 16 = 14 sixteenths.
- How do I convert feet and inches to decimal feet?
- Divide the inches by 12 and add them to the feet. 12' 7 1/2" is 12 + 7.5 ÷ 12 = 12.625 ft, which is what the room fields of a flooring or square footage calculator expect.
- How do I read a tape measure?
- Find the last whole inch before the end of what you are measuring, then count the small marks after it. On a tape marked in 16ths, the longest mark between two inches is 1/2, the next longest are the 1/4s, then the 1/8s, and the shortest are the 1/16s. Three 1/16 marks past 7 inches is 7 3/16". Many tapes also print a small foot number or a red box every 12 inches (16" on some, for stud spacing).
- Why does 170 cm come out as 5' 6 15/16"?
- Because an inch is exactly 25.4 mm, 170 cm is ≈ 66.9291 inches, which falls between two 1/16 marks. The calculator shows the nearest one, 5' 6 15/16", and says how far that is from the exact length: ≈ 0.0084 in (0.2125 mm) longer than the exact ≈ 66.9291 in. Choose 1/32 or 1/64 for a closer fraction.
- How precise should I be: 1/8, 1/16 or 1/32?
- Framing and rough carpentry usually work to 1/8 inch, trim and cabinetry to 1/16, and fine woodworking to 1/32 or better. A standard tape is marked to 1/16 (some to 1/32 for the first foot), so rounding to 1/16 gives numbers you can actually find on it.
- How do I write feet and inches?
- A single prime or apostrophe means feet and a double prime or quote means inches: 5' 7 3/8". Plans often put a hyphen between them (5'-7 3/8"). This calculator also reads 5ft 7-3/8in, 5 feet 7 and 3/8 inches, 67.375 in, 67 3/8 and metric such as 170 cm or 1 m 20 cm.
- Can I multiply or divide two lengths?
- Yes. A length times a number repeats it (5' 7 3/8" × 3), and a length times a length gives an area in square feet. A length divided by a number splits it into equal parts; a length divided by a length says how many fit: 12' 6" ÷ 16" = 9.375, so 9 whole lengths fit, with 6" left over.
How it works
Every length you type is converted to an exact fraction of an inch: feet are 12 inches, yards 36, and metric lengths use the exact definition 1 inch = 25.4 mm, so 1 mm is 5/127 inch. Adding, subtracting, multiplying and dividing keep those fractions exact (with whole numbers of any size), so nothing drifts the way floating-point decimals can. Only the answer you see is rounded: the feet and inches to the nearest fraction you choose, halves rounding away from zero, with the difference from the exact length given in inches and millimetres; decimals are shown in full up to six places and otherwise to four, marked ≈. The tape strip draws the inch the answer falls in, with the marks a 1/16 (or 1/32) tape has. A number with no unit is read in the unit you pick under "Plain numbers are". Everything runs in your browser.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (1 inch = 2.54 cm exactly)
- Refinement of values for the yard and the pound, Federal Register, 1 July 1959 (the international inch)
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