Feet & Inches Calculator
Perform arithmetic on measurements in feet, inches, and fractional inches. Perfect for construction and woodworking.
Reviewed by the ToolNestr Editorial Team — July 2026
How feet and inches arithmetic works
The imperial measurement system, used primarily in the United States and to some extent in the UK and Canada, expresses length in feet and inches where one foot equals 12 inches. Performing arithmetic on these mixed units can be tedious by hand. This calculator converts both measurements entirely to inches, performs the operation, then converts the result back to feet and inches for display.
Each measurement is parsed as feet plus inches (with decimal inches supported). The total in inches is computed as (feet × 12) + inches. The operation runs on the inch totals, and the result is decomposed back: divide by 12 for feet, with the remainder as inches. When the remainder is exactly zero, the result shows whole feet.
The formula explained
Worked example
5 ft 8 in + 3 ft 4 in
Woodworking
Add board lengths, subtract kerf widths, and calculate total material needed for a project without mental math errors.
Construction Layout
Add wall lengths, subtract window and door openings, and verify overall dimensions match the architectural plan.
Interior Design
Add furniture dimensions to verify they fit in a room. Subtract clearance requirements from available space.
DIY Projects
Measure twice, cut once. Use the calculator to add up all the pieces you need for fencing, decking, or shelving.
How to use the feet and inches calculator
Enter measurements
Type the feet and inches for each measurement. Inches can include decimals for fractional precision.
Choose operation
Select add, subtract, or multiply. Each uses the internal inch representation for precise results.
Read the result
See the total in inches and the decomposed feet + inches format simultaneously.
Tips for feet and inch calculations
Always measure twice
Small errors in feet and inches compound quickly. Double-check your input values against a physical tape measure.
Use decimals for fractions
A half inch is 0.5, a quarter is 0.25, an eighth is 0.125. For exact fractional inches, use the inches to fraction calculator.
Multiplication gives area
When you multiply two length measurements, the result is in square inches. Divide by 144 to get square feet.
Related tools
Frequently asked questions
How many inches are in a foot?
12 inches = 1 foot. The calculator handles this conversion automatically.
Can I use fractions of an inch?
Yes. Enter fractions as decimals (e.g., 0.5 for 1/2 inch). The result includes the decimal inch equivalent.
Does it handle negative results?
Yes. If subtraction gives a negative result, it is shown with a minus sign.
What is the maximum value?
There is no hard limit, but very large numbers may display in scientific notation.
Can I multiply feet and inches?
Yes. Select multiply to multiply the two measurements together, useful for area calculations.