Feet and Inches Calculator
Enter measurements the way they're written on the plans — 12' 7 3/8", 150mm or plain decimals — then add, subtract, multiply or divide them. The answer snaps to real tape-measure fractions and shows every conversion step.
The formula
Every measurement is normalized to inches first: feet × 12 + whole inches + fraction (numerator ÷ denominator). Metric inputs are converted at exactly 25.4 mm per inch. Arithmetic runs on those inch values; results convert back to feet-inches-fractions by snapping to your chosen precision (1/2" to 1/64").
Worked example: 12' 7⅜" + 5½" → 151.375 + 5.5 = 156.875 in → 13' 0⅞".
Fraction precision
| Precision | Typical use |
|---|---|
| 1/2" | Rough framing estimates |
| 1/4" | Carpentry layout |
| 1/8" | Framing and trim |
| 1/16" | Tape measure standard — default here |
| 1/32", 1/64" | Fine woodworking |
Frequently asked questions
- How do I type feet and inches?
- Any of these work:
12' 7 3/8",12'7-3/8",12ft 7 3/8in,151.375. Plain numbers use the unit selector. - What does multiplying two measurements give?
- An area in square inches (with square feet below it). Dividing gives a dimensionless ratio — useful for pitch conversions like rise ÷ run.
- Why does the result sometimes jump to a "rounder" number?
- Results snap to your selected fraction precision so you can read them off a tape. Switch to 1/64" for maximum resolution.