Feet and Inches Calculator
Enter two measurements in feet and inches, choose an operation, and get the result in feet-and-inches, decimal feet, total inches, centimeters, and millimeters. Inches can be whole numbers, decimals, or fractions like 3/8 or 1 1/4. Results update as you type.
How to add feet and inches
To add two measurements in feet and inches, convert each one to total inches first: multiply the feet by 12 and add the inches. Then add the two totals. Finally, divide the sum by 12 to get whole feet and take the remainder as inches. For example, 5 ft 9 in plus 3 ft 4 in is (5x12+9) + (3x12+4) = 69 + 40 = 109 inches. Dividing by 12 gives 9 ft with a remainder of 1 in, so the answer is 9 ft 1 in. This calculator handles all the steps for you, including fractional inches.
How to subtract feet and inches
Subtraction follows the same approach. Convert each measurement to total inches, subtract the smaller from the larger, then convert the result back to feet and inches. If the second measurement is larger than the first the result is negative, which can mean you need to trim more material than you have, or the gap is wider than the board. This calculator clearly flags negative results so you can spot measurement errors before cutting.
Multiplying and dividing feet and inches
Multiplying two lengths (for example, the width and length of a room) produces an area, not a length. The result is given in square feet (ft²) and square inches (in²). This is useful for floor, ceiling, or wall area estimates before ordering materials. Dividing one length by another gives a dimensionless ratio, useful for scale factors, slope calculations, or checking proportions. The calculator labels each result so you always know the unit.
Converting feet and inches to metric
One inch equals exactly 2.54 centimeters and 25.4 millimeters. One foot equals 30.48 cm or 304.8 mm. To convert a feet-and-inches measurement to centimeters, multiply the total number of inches by 2.54. This calculator does that automatically every time you calculate, so you get the metric equivalent alongside the imperial result without any extra steps.
Fraction precision and tape measures
Tape measures are typically marked in increments of 1/16 inch for general construction, 1/32 inch for woodworking, and occasionally 1/64 inch for precision joinery. The fraction precision selector on this calculator lets you round the fractional-inch part of the result to match the smallest graduation on your tape measure, so the number you read off the screen matches the mark you will find on the tape.
Feet and inches conversion reference
| Fraction | Decimal inches | Centimeters | Millimeters |
|---|---|---|---|
| 1/16" | 0.0625 | 0.159 | 1.6 |
| 1/8" | 0.125 | 0.318 | 3.2 |
| 1/4" | 0.25 | 0.635 | 6.4 |
| 3/8" | 0.375 | 0.953 | 9.5 |
| 1/2" | 0.5 | 1.270 | 12.7 |
| 3/4" | 0.75 | 1.905 | 19.1 |
| 1" | 1.0 | 2.540 | 25.4 |
| 6" | 6.0 | 15.24 | 152.4 |
| 1 ft (12") | 12.0 | 30.48 | 304.8 |
Common inch fractions and their decimal and centimeter equivalents.
Frequently asked questions
How do I add feet and inches manually?
Convert both measurements to total inches by multiplying feet by 12 and adding the inches. Sum the two totals. Then divide by 12: the quotient is feet and the remainder is inches. For example, 6 ft 3 in + 2 ft 11 in = 75 + 35 = 110 in = 9 ft 2 in.
What does the multiply mode calculate?
When you multiply two lengths in feet and inches, the result is an area. For example, a room 12 ft 6 in wide and 15 ft 0 in long has an area of 12.5 x 15 = 187.5 square feet. The calculator shows the result in square feet and square inches.
Can I enter fractional inches like 3/8 or 1 3/4?
Yes. Enter the fractional part directly in the Inches field as a decimal (0.375 for 3/8") or type the decimal equivalent. The calculator also accepts the decimal inch directly, so 1.75 means 1 and 3/4 inches. For common fractions, use the reference table to find the decimal equivalent.
How do I convert feet and inches to centimeters?
Multiply the total number of inches by 2.54. So 5 ft 9 in = 69 inches x 2.54 = 175.26 cm. The calculator does this conversion automatically and also shows millimeters (multiply total inches by 25.4).
What fraction precision should I use?
Match the smallest graduation on your tape measure. Standard construction tape measures show 1/16". Woodworking and cabinet tapes often show 1/32". Precision joinery or machinist rules may show 1/64". Selecting the right precision makes it easy to transfer the result directly to the tape without rounding mentally.
What does a negative result mean?
A negative result from subtraction means the second measurement is larger than the first. In practice, this could mean a board is shorter than needed, or a gap is wider than the piece you plan to insert. Check your measurements and decide whether to swap the values or order additional material.
How many inches are in a foot?
There are exactly 12 inches in 1 foot. This is the fundamental conversion: to go from feet to inches multiply by 12, and to go from inches to feet divide by 12. One foot equals 30.48 centimeters.