How to add feet and inches
Type a measurement the way you'd write it on a board, like 9' 7 1/2, and press Add. Keep adding or subtracting. The running total stays in feet-inches-fractions, rounded to the precision you pick (1/8", 1/16" or 1/32").
By hand, it works like this:
- Convert everything to inches: 9' 7½" = 108 + 7.5 = 115.5". 3' 4⅝" = 36 + 4.625 = 40.625".
- Add or subtract: 115.5 + 40.625 = 156.125".
- Convert back: 156.125 ÷ 12 = 13 feet with 0.125" left over, so 13'-0 1/8".
Rounding to a fraction
Decimals become fractions by rounding to the nearest 1/16" (or 1/8", 1/32"): multiply the decimal part by 16 and round. 0.38" × 16 = 6.08, so 6/16, which reduces to ⅜". Pick 1/8" for rough framing and 1/16" or 1/32" for trim and stair work.
Need more than add and subtract?
The construction calculator has the full keypad: multiply and divide feet-inches, memory, and framing keys for rise, run, pitch, diagonal, hips, stairs, jacks and rake walls.
FAQ
How do you add feet and inches with fractions?
Convert each measurement to inches (feet × 12 + inches + fraction), add them, then divide the total by 12. The whole number is feet and the remainder is inches. Round the leftover decimal to the nearest 1/16".
How do I convert decimal inches to fractions?
Multiply the decimal part by 16 (for sixteenths) and round to a whole number, then reduce. 0.8125 × 16 = 13, so 0.8125" is 13/16".
How do I enter feet and inches in this calculator?
Type them the way you write them: 9' 7 1/2, 10'-3, 115 (inches), 7 3/4, or 16' for an even 16 feet. A plain number is read as inches.
Can I subtract measurements?
Yes. Type the length and press Subtract. That is handy for cut lengths, like a wall height minus plates, or an opening minus jamb and shim space.