Feet inch calculator
Add, subtract, multiply and divide feet, inches and fractions of an inch.
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Type a measurement the way it is written on a plan or a tape, such as 5' 7 3/8", and the answer comes back in feet, inches and a fraction, with decimal feet, decimal inches, millimeters and meters beside it.
How to type a measurement
The ′ key is feet, the ″ key is inches, the space key separates whole inches from a fraction, and the fraction keys add a space and the fraction for you. A physical keyboard works too: use the apostrophe and quote keys. Press = for the answer, then press a sign to keep calculating from it.
| You type | It reads |
|---|---|
| 5' 7 3/8" | 5 feet, 7 and 3/8 inches |
| 67 3/8" | 67 and 3/8 inches |
| 5'-7 3/8" | 5 feet, 7 and 3/8 inches (the dash is allowed) |
| 5.5' | 5 and a half feet |
| 3/4" | three quarters of an inch |
| 1700 mm, 170 cm, 2.35 m | metric lengths |
| 12 | a plain number, used as a multiplier or divisor. Added to or subtracted from a length it counts as inches. |
A length times a length is an area, and an area times a length is a volume. 2' 6" × 4' shows 10.00 sq ft, and times 6" it shows 5.00 cu ft. A length divided by a length is a plain number: 9' ÷ 3' is 3.
How to add feet and inches by hand
To add feet and inches, add the feet to the feet and the inches to the inches, then turn every 12 inches into 1 foot. When the inches include fractions, add the fractions first over a common denominator and carry any whole inches into the inch total.
5' 7 3/8" + 2' 9 15/16"
- Feet: 5 + 2 = 7.
- Fractions: 3/8 = 6/16, and 6/16 + 15/16 = 21/16 = 1 5/16. Keep 5/16 and carry 1 inch.
- Inches: 7 + 9 + 1 (carried) = 17.
- 17 inches is 1 foot 5 inches, so the feet become 7 + 1 = 8 and the inches 5.
- Answer: 8' 5 5/16".
How to subtract feet and inches by hand
Subtract the feet from the feet and the inches from the inches. If the inches on top are smaller than the inches below, borrow 1 foot from the feet and add 12 inches to the inches.
8' 5 5/16" − 2' 9 15/16"
- 5 5/16 is less than 9 15/16, so borrow 1 foot: 8' 5 5/16" becomes 7' 17 5/16".
- Inches: 17 5/16 − 9 15/16 = 7 6/16 = 7 3/8.
- Feet: 7 − 2 = 5.
- Answer: 5' 7 3/8".
How to multiply and divide feet and inches by hand
Change each length to inches, multiply or divide, then change the answer back. Two lengths multiplied give an area, so divide square inches by 144 to get square feet.
2' 6" × 4': 30 in × 48 in = 1,440 sq in. 1,440 ÷ 144 = 10 sq ft.
10' 6" ÷ 4: 126 in ÷ 4 = 31 1/2 in = 2' 7 1/2".
9' ÷ 3': 108 in ÷ 36 in = 3, a plain number.
Feet and inches to decimal feet and decimal inches
For decimal feet, divide the inches by 12 and add the feet: 5' 7 3/8" is 5 + 7.375 / 12 = 5.615 ft. For decimal inches, multiply the feet by 12 and add the inches: 5 × 12 + 7.375 = 67.375 in. To get millimeters, multiply inches by 25.4: 67.375 in is 1,711.3 mm.
| Fraction | Decimal inches | Millimeters |
|---|---|---|
| 1/16" | 0.0625 | 1.5875 |
| 1/8" | 0.125 | 3.175 |
| 3/16" | 0.1875 | 4.7625 |
| 1/4" | 0.25 | 6.35 |
| 5/16" | 0.3125 | 7.9375 |
| 3/8" | 0.375 | 9.525 |
| 7/16" | 0.4375 | 11.1125 |
| 1/2" | 0.5 | 12.7 |
| 9/16" | 0.5625 | 14.2875 |
| 5/8" | 0.625 | 15.875 |
| 11/16" | 0.6875 | 17.4625 |
| 3/4" | 0.75 | 19.05 |
| 13/16" | 0.8125 | 20.6375 |
| 7/8" | 0.875 | 22.225 |
| 15/16" | 0.9375 | 23.8125 |
How the rounding works
Every calculation is done with exact fractions, so no error builds up from step to step. Only the result on screen is rounded, to the nearest 1/16 inch by default, or to 1/2, 1/4, 1/8, 1/32 or 1/64 if you change the setting. A tape measure usually marks 1/16 inch. When the shown result is rounded, the line under it says so and gives the exact value.
Two examples: 11 63/64" rounds up to 1' 0" at 1/16, and 108" ÷ 14 is exactly 7 5/7" but shows as 7 11/16".
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The same calculator is being built as an app for iPhone and Android.
Questions
How do I add feet and inches?
Add the feet to the feet and the inches to the inches, then turn every 12 inches into 1 foot. If the inches have fractions, add the fractions first over a common denominator and carry any whole inches. For example, 5' 7 3/8" + 2' 9 15/16" = 8' 5 5/16".
How do I subtract feet and inches when the inches are too small?
Borrow 1 foot, which is 12 inches, and add it to the inches. To subtract 2' 9 15/16" from 8' 5 5/16", write 8' 5 5/16" as 7' 17 5/16", then subtract: 5' 7 3/8".
How do I convert feet and inches to decimal feet?
Divide the inches by 12 and add the result to the feet. 5' 7 3/8" is 5 + 7.375 / 12 = 5.615 feet. To get decimal inches instead, multiply the feet by 12 and add the inches: 67.375 in.
How do I turn a fraction of an inch into a decimal?
Divide the top number by the bottom number: 3/8 is 3 / 8 = 0.375 in. The table on this page lists every sixteenth of an inch with its decimal value and its size in millimeters.
What does rounding to 1/16 inch mean?
The calculator keeps the exact value and rounds only what it shows, to the nearest 1/16 inch by default. You can pick 1/2 to 1/64. When the shown value is rounded, the calculator says so and gives the exact value, for example 108" divided by 14 is exactly 7 5/7" and shows as 7 11/16".
Can I enter metric lengths?
Yes. Type a number followed by mm, cm or m, such as 1700 mm or 2.35 m. You can mix metric and feet-inch lengths in one calculation, and every result also shows millimeters and meters.
Can the iPhone calculator do feet and inches?
The built-in Calculator app on iPhone has no feet or inch keys, so you have to convert each length to inches or decimals first and convert the answer back. This calculator takes feet, inches and fractions as typed.
Is anything I type saved or sent?
No. The calculation runs in your browser and nothing you type is uploaded.