Tape-measure numbers do not play well with a regular calculator: 5’ 7 3/8” mixes three units — feet, inches and fractions of an inch — in base 12 and base 16. This calculator reads measurements the way you write them on a cut list, does the arithmetic exactly, and gives the answer back in feet, inches and sixteenths, along with decimal and metric equivalents.
How to use the feet and inches calculator
- Type the first measurement, such as
5' 7 3/8",5ft 7-3/8in,67.375"or12'. - Choose an operation: add or subtract another length, multiply or divide by a plain number, or find how many times one length fits into another.
- Enter the second measurement or the number.
- Choose the rounding — 1/16” suits most tape measures — and read the result.
A bare number with no ’ or “ mark is read as inches, so 16 means 16 inches.
How feet-and-inches math works
Everything is converted to inches, calculated, then converted back:
The fractional part of the remaining inches is rounded to the nearest 1/16 (or whatever you choose) and reduced, so 8/16 shows as 1/2 and 12/16 as 3/4. If the rounding carries the inches up to 12, the result rolls over to the next foot.
Worked examples
Add: 5' 7 3/8" + 3' 10 15/16" → 67.375 + 46.9375 = 114.3125 in. 114.3125 ÷ 12 = 9 feet with 6.3125 in left, and 0.3125 = 5/16, so the answer is 9' 6 5/16".
Divide into equal parts: 5' 7 3/8" ÷ 3 = 22.4583 in, which rounds to 1' 10 7/16" (off by about 0.02 in).
How many fit: 12' 6" ÷ 16" = 150 ÷ 16 = 9.375 — nine full 16-inch spaces with 6 inches left over.
Fractions of an inch as decimals
| Fraction | Decimal inch | Fraction | Decimal inch |
|---|---|---|---|
| 1/16 | 0.0625 | 9/16 | 0.5625 |
| 1/8 | 0.125 | 5/8 | 0.625 |
| 3/16 | 0.1875 | 11/16 | 0.6875 |
| 1/4 | 0.25 | 3/4 | 0.75 |
| 5/16 | 0.3125 | 13/16 | 0.8125 |
| 3/8 | 0.375 | 7/8 | 0.875 |
| 7/16 | 0.4375 | 15/16 | 0.9375 |
| 1/2 | 0.5 | 1 | 1.0 |
Every sixteenth adds 0.0625 inch, which is about 1.6 millimeters.
Tips for accurate cut lists
- Account for the saw kerf. A typical circular-saw blade removes about 1/8 inch per cut. When dividing a board into equal pieces, subtract one kerf for each cut before dividing.
- Avoid compounding rounding. Add up exact measurements first and round once at the end; rounding each piece separately can drift by a sixteenth per piece.
- Mark from one end. Cumulative marks measured from a single reference point are more accurate than measuring each piece from the last mark.
- Convert for area and volume. For square footage of floors and walls, the square footage calculator takes decimal feet; for lumber, the board foot calculator prices boards by volume.
Frequently asked questions
How do I add feet and inches?
Convert each measurement to inches (feet × 12 plus inches), add them, then convert back by dividing by 12: the whole number is feet and the remainder is inches. For example, 5' 7 3/8" + 3' 10 15/16" = 67.375 + 46.9375 = 114.3125 inches = 9' 6 5/16".
How do I convert inches to feet and inches?
Divide by 12. The whole-number part is feet and the remainder is inches. 100 inches ÷ 12 = 8 remainder 4, so 100 inches is 8' 4".
How do I type fractions of an inch?
Leave a space or a hyphen between the whole inches and the fraction: 7 3/8" or 7-3/8". Feet take an apostrophe ('), and inches a double quote ("). You can also write ft and in, or use decimals such as 7.375".
What does rounding to the nearest 1/16 inch mean?
Most tape measures are marked in sixteenths of an inch, so the calculator rounds results to the closest mark. Dividing 67 3/8 inches into three equal parts gives 22.458 inches, which rounds to 22 7/16 inches. Choose 1/32 or 1/64 for finer work.
How do I convert decimal feet to feet and inches?
Multiply the decimal part by 12. For 7.35 feet, 0.35 × 12 = 4.2 inches, so it is 7' 4.2", or about 7' 4 3/16" to the nearest sixteenth.