Square Footage Calculator

How it works

Square footage is the area of a space measured in square feet — the standard unit for residential and commercial real estate in the US. The formula is straightforward: length × width = area. For a rectangular room, measure both dimensions in feet (decimal feet, not feet+inches) and multiply.

This calculator outputs the same area in four common units: square feet (ft²), square yards (yd² — used for carpeting), square meters (m² — used internationally), and acres (used for land). Multiplying ft² by 0.0929 gives m²; dividing by 9 gives yd²; dividing by 43,560 gives acres.

For non-rectangular spaces, divide the area into rectangles, triangles, or circular segments. A triangle's area is (base × height) / 2. A circle is π × radius². An L-shaped room is two rectangles. Sum the parts to get the total area.

Common uses: pricing flooring (sold by ft² or yd²), pricing painting (cost per ft² of wall), real-estate valuation ($/ft² of livable space), and HVAC sizing (BTUs needed = area × insulation factor). Carpeting almost always charges by yd² in the US — divide ft² by 9 to convert.

Watch out for "gross" vs "net" floor area. Listed home square footage typically excludes garages, attics, and finished basements; these may add value but are reported separately. ANSI Z765 is the US standard for measuring residential floor area — measure the exterior of finished space at floor height.

Don't forget to account for waste in materials. Flooring, tile, and roofing all need 5–15% extra to cover cut waste, defects, and unusual angles. For irregular rooms, add closer to 15%; for simple rectangles, 5–10% is plenty.