Feet and Inches Length Calculator

A feet and inches length calculator adds or subtracts two lengths given in feet and inches. It converts each length to total inches, does the math, and converts the result back to feet and inches. For 5 ft 3.5 in. plus 2 ft 7.75 in., the sum is 7 ft 11.25 in.

Last reviewed September 2026Method & sources Report an error

Feet

Breakdown
Feet	7
Inches	11.2500 in
Total (all in inches)	95.2500 in

How to Calculate Feet and Inches Length

Both lengths are converted to a single total-inches figure (`feet × 12 + inches`). That makes addition or subtraction a simple arithmetic operation, without needing to carry or borrow across the feet/inches boundary by hand. The result converts back to feet and inches by dividing by 12 (whole feet) and taking the remainder (inches).

Example: 5 ft 3-1/2 in. plus 2 ft 7-3/4 in.

5 ft 3-1/2 in. plus 2 ft 7-3/4 in.: 1. Length 1 in total inches: (5 × 12) + 3.5 = 63.5 in. 2. Length 2 in total inches: (2 × 12) + 7.75 = 31.75 in. 3. Sum: 63.5 + 31.75 = 95.25 in. 4. Back to feet and inches: 95.25 ÷ 12 = 7 remainder 11.25, so 7 ft 11-1/4 in.

What Is Feet and Inches Length?

A feet and inches length calculator adds or subtracts two measurements given in the mixed feet-and-inches format common in US construction and carpentry. It handles the awkward carrying and borrowing across the 12-inch boundary, which makes this arithmetic error-prone by hand or with a plain decimal calculator.

Feet and Inches Length: Pros and Cons

Pros

Handles the feet/inches carrying and borrowing automatically, avoiding a common source of manual arithmetic error
Works for both addition and subtraction
Reports the result in both feet-and-inches and a single total-inches figure, useful depending on what you need next

Cons

Inches are entered as a decimal (e.g., 3.5 for 3-1/2 in.) rather than as a fraction directly. See the Inch Fraction calculator for converting a common fraction to its decimal equivalent first
A subtraction result that would be negative (length 2 longer than length 1) is clamped to zero, since a negative physical length isn't meaningful. Reorder the inputs if you need to know by how much the second length exceeds the first
Handles two lengths at a time. Adding several measurements together needs the result of one calculation fed into the next as one of its inputs

Feet and Inches Length: What a Pro Checks

Convert a fraction to its decimal equivalent before entering it. This calculator expects decimal inches (3.5 for 3-1/2 in.), not a fraction directly.
If you need to know by how much a shorter length falls short of a longer one, swap the two lengths' order and subtract again. A result that would go negative is clamped to zero instead of showing the difference.
To add more than two measurements, chain the calculations. Add the first two, then use that total as one of the inputs for the next pair, repeating until everything is combined.

Frequently Asked Questions

How do I add feet and inches together?

Convert both measurements entirely to inches (feet × 12 + inches), add the totals, then convert back to feet and inches by dividing by 12. 5 ft 3.5 in. plus 2 ft 7.75 in. equals 7 ft 11.25 in.

How do I enter a fraction like 3/8 inch?

Enter it as its decimal equivalent. 3/8 in. is 0.375. Common fraction-to-decimal conversions: 1/2 = 0.5, 1/4 = 0.25, 3/4 = 0.75, 1/8 = 0.125, 3/8 = 0.375, 5/8 = 0.625, 7/8 = 0.875, 1/16 = 0.0625.

What happens if I subtract a longer length from a shorter one?

The result is clamped to zero, since a negative physical length isn't meaningful here. If you need to know by how much the second length exceeds the first, swap the order of the two lengths and subtract again.

Why is this arithmetic harder than regular decimal math?

Because feet and inches aren't a base-10 system relative to each other. 12 inches make a foot, not 10. So adding or subtracting mixed feet-and-inches measurements by hand requires carrying or borrowing across that 12-inch boundary, which is easy to get wrong, especially with fractional inches involved.

Can I add more than two lengths at once?

Not directly in one step. Add the first two lengths, then use that result as one of the two inputs for a second calculation with the next length, repeating until all lengths are combined.

Measurement