Feet-Inches Fraction Calculator
Add, subtract, and convert tape-measure numbers — feet, inches, and sixteenths — without decimal headaches.
Measurement A
ftin
Measurement B
ftin
Result
9′ 4 1/8″
= 112.125 in = 284.8 cm
Tape history
5′ 9 3/8″ + 3′ 6 3/4″ = 9′ 4 1/8″
8′ 0″ − 2′ 3 1/2″ = 5′ 8 1/2″
16 1/8″ × 4 = 5′ 4 1/2″
8′ 0″ − 2′ 3 1/2″ = 5′ 8 1/2″
16 1/8″ × 4 = 5′ 4 1/2″
Common conversions
1/16″ = 0.06251/2″ = 0.51/8″ = 0.1255/8″ = 0.6251/4″ = 0.253/4″ = 0.753/8″ = 0.3757/8″ = 0.875
How it works
Tape-measure math is base-12 and base-16 at once — twelve inches to a foot, sixteenths within the inch — which is exactly why it trips people up. The calculator converts each measurement to a single number of inches, does the arithmetic there, then converts back to feet, inches, and the nearest sixteenth.
Add and subtract combine two measurements. Multiply and divide scale one measurement by the number in the second box, which is how you handle "six treads at 10 3/16 each" or splitting a board into equal parts. Every result also shows plain decimal inches and centimeters for when you need to leave tape units behind.
Worked example
5′ 9 3/8″ + 3′ 6 3/4″
= 69.375 in + 42.75 in = 112.125 in
= 9′ 4 1/8″ = 284.8 cm
= 69.375 in + 42.75 in = 112.125 in
= 9′ 4 1/8″ = 284.8 cm
Questions about tape math
Convert each measurement to inches (feet × 12 + inches + fraction), add them, then carry every 12 in back into a foot. 5′ 9 3/8″ + 3′ 6 3/4″ is 69.375 + 42.75 = 112.125 in, which is 9′ 4 1/8″.
Divide by 12. The whole number is feet; multiply the remainder by 12… no — the remainder already is inches. 112 in ÷ 12 = 9 feet with 4 in left over, so 112 in = 9′ 4″.
Multiply the decimal part by 16 and round to the nearest whole number of sixteenths, then reduce. 0.375 × 16 = 6/16 = 3/8. This calculator does it to the nearest 1/16 in by default.
You can, and the calculator shows the decimal alongside every answer. But your tape is marked in sixteenths, so a cut list in feet-inches-sixteenths is what you actually carry to the saw.