Feet & Inches Calculator
Convert feet and inches to total inches, decimal feet, and centimeters — or add and subtract two measurements.
A feet-and-inches calculator with two modes: convert a measurement to total inches, decimal feet, centimeters, and meters, or add/subtract two measurements (like 5'10" + 2'6") with the result normalized back to feet and inches. Built for DIY, carpentry, and height math.
How to use this calculator
- Step 1: Choose Convert or Add / Subtract mode.
- Step 2: Enter feet and inches (decimals allowed).
- Step 3: In math mode, enter the second measurement and pick + or −.
- Step 4: Click Calculate to see total inches, decimal feet, and metric equivalents.
The formula
total inches = feet × 12 + inches; cm = inches × 2.54 (exact)
Worked example
6 feet 2 inches equals 74 inches, 6.1667 decimal feet, and 187.96 cm. Adding 6'2" and 5'9" gives 11'11".
Frequently Asked Questions
How do I convert feet and inches to decimal feet?
Divide the inches by 12 and add the feet: 5'10" is 5 + 10/12 = 5.8333 feet. Decimal feet are what most construction calculators and cutting lists expect, since you can't easily do arithmetic on the feet'inches" format.
How do I add two measurements in feet and inches?
Convert both to total inches, add, then convert back: 5'10" (70") + 2'6" (30") = 100" = 8'4". Doing it in total inches avoids the carry errors that happen when you add the feet and inches columns separately and forget that inches roll over at 12, not 10.
How many centimeters are in an inch?
Exactly 2.54 cm — the international inch has been defined this way since 1959. So 70 inches is exactly 177.8 cm. This calculator uses the exact definition, not an approximation.
Why does subtracting give an error for a negative result?
Lengths can't be negative in the physical world this tool is built for, so instead of showing −2'3" it asks you to put the larger measurement first. If you actually need a signed difference (e.g. how short a board is), subtract the smaller from the larger and note the direction yourself.
Can I enter fractional inches like 10.5?
Yes — decimal inches work everywhere in this calculator, in both convert and add/subtract modes. Carpenters who think in fractions can enter 10.5 for 10½". (A dedicated fraction display is on the roadmap.)