How this calculator works
The calculator turns each length into inches (feet × 12, plus inches, plus the fraction), does the arithmetic in inches, and then shows the answer in feet, inches and sixteenths, which is how a tape measure reads. Adding and subtracting need a second length; multiplying and dividing use a plain number; and "divide by B" tells you how many times B fits in A.
Worked example: 5 ft 7½ in is 67.5 inches and 2 ft 8¾ in is 32.75 inches. Added they make 100.25 inches, which is 8 ft 4 1/4 in. Subtracted they make 2 ft 10 3/4 in. Multiplying 5 ft 7½ in by 3 gives 16 ft 10 1/2 in, dividing by 4 gives 1 ft 4 7/8 in, and 2 ft 8¾ in fits into 5 ft 7½ in 2.06 times.
Inches to decimals and millimeters
Fractions of an inch that a tape measure shows.
| Fraction | Decimal inches | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 | 1.59 |
| 1/8 in | 0.1250 | 3.17 |
| 3/16 in | 0.1875 | 4.76 |
| 1/4 in | 0.2500 | 6.35 |
| 5/16 in | 0.3125 | 7.94 |
| 3/8 in | 0.3750 | 9.52 |
| 7/16 in | 0.4375 | 11.11 |
| 1/2 in | 0.5000 | 12.70 |
| 9/16 in | 0.5625 | 14.29 |
| 5/8 in | 0.6250 | 15.88 |
| 11/16 in | 0.6875 | 17.46 |
| 3/4 in | 0.7500 | 19.05 |
| 13/16 in | 0.8125 | 20.64 |
| 7/8 in | 0.8750 | 22.22 |
| 15/16 in | 0.9375 | 23.81 |
Tips before you buy
- Measure twice, add up once. Write each measurement down in feet, inches and fraction, and add the fractions first.
- To find the number of equal spaces in a length, use "divide A by B".
- Remember that a 2×4 is really 1½ × 3½ inches and a 1×6 is ¾ × 5½ inches when you work out how many boards fit.
- A tape measure reads in sixteenths, so a result to the nearest 1/16 inch is as precise as you can mark.
- For metric, use the decimal inches or the millimeters row, and mark them on a metric tape.
Tools & materials for this project
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Frequently asked questions
How do you add feet and inches?
Convert both lengths to inches, add them, and convert back: 5 ft 7½ in plus 2 ft 8¾ in is 67.5 + 32.75 = 100.25 inches, or 8 ft 4 1/4 in. This calculator does it for you, and rounds to the nearest 1/16 inch.
How do you subtract feet and inches?
Convert to inches, subtract, and convert back: 5 ft 7½ in minus 2 ft 8¾ in is 2 ft 10 3/4 in.
How do you multiply feet and inches?
Multiply the length in inches by the number, then convert back to feet and inches: 5 ft 7½ in × 3 is 16 ft 10 1/2 in.
How many inches are in a foot?
12. A tape measure is marked in sixteenths of an inch, so a 1/16 inch is 0.0625 in or about 1.59 mm.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.