Rectangle Area Difference Calculator

Compare two rectangular areas from their lengths and widths. The result is the second rectangle’s area minus the first rectangle’s area.

How to use Rectangle Area Difference Calculator

1. Choose Measurement Unit, then enter First Length, First Width, Second Length, Second Width without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read area difference. 4. Select Select Copy result to copy the answer, or Reset to clear the form.

Why use this tool?

See how much usable area changes between two room, panel or layout dimensions without subtracting the side lengths individually.

How the calculation works

Area difference = second length × second width − first length × first width. All four lengths use the same unit. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas

Example

A first rectangle of 12 × 8 cm has area 96 cm². A second rectangle of 15 × 8 cm has area 120 cm², so the difference is 24 cm².

Practical tip

The two rectangles may have different proportions. The result compares their total areas rather than a particular border width.