By Chris Deziel
Updated Aug 30, 2022
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Calculating the square footage of a rectangle is simply determining its area—a fundamental skill in many real‑world contexts. Whether you’re a homeowner planning a garden, a contractor estimating flooring, or a painter gauging wall space, knowing the area is essential. The process requires two measurements—length and width, both in feet—multiplied together.
TL;DR: The area of a rectangle, A, is the product of its length, L, and its width, W. Formula: A = L × W.
Before you perform any calculation, confirm the space is truly rectangular: the two longer sides must be equal, as must the two shorter sides. Measure each side with a tape measure. If one pair of opposing sides differs significantly, treat the area as a composite shape—divide it into a rectangle and a triangle (or other shape), calculate each area separately, then sum the results.
Once the shape is verified, follow these steps:
Use a tape measure or ruler to record the length and width in feet and inches.
For simplicity, convert inches to a decimal fraction of a foot: divide the number of inches by 12. For example, 5" = 5/12 = 0.42 ft, so 13′5" becomes 13.42 ft. This step is optional but eliminates cumbersome fractional multiplication.
Multiply the decimal length by the decimal width to obtain the square footage.
Example: A homeowner wants to know how many square feet a living room floor covers. The floor measures 17′7" by 12′3". Converting to decimals gives 17.58 ft × 12.25 ft = 215.36 sq ft.
