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What is the formula for floor space?

The core formula is length x width, applied per rectangular section and summed. For a simple rectangular room: floor space = length (ft) x width (ft), giving square feet. For irregular spaces, decompose the shape: split an L-shaped room into two rectangles, calculate each, and add them. Triangular sections use (base x height) / 2, and circular areas use pi x radius squared.

For a whole home's gross living area, the standard practice (ANSI Z765) is to measure to the exterior wall faces, include finished, heated, above-grade space, and exclude garages, unfinished basements, and open areas like two-story foyers on the upper level. Converting units: divide square feet by 10.764 to get square meters.

The formula itself is trivial; the errors come from measurement and decomposition, especially with angled walls, curved bays, and rooms that aren't true rectangles. That's where digital tracing beats hand calculation. MeasureFloorPlan computes exact areas for any traced shape on a scaled floor plan, so complex outlines don't have to be broken into rectangles at all.