Square Footage Calculator
Calculate total square footage for one or more equal rectangular areas, with an optional waste allowance.
Planning estimate only. Verify product specifications, field measurements, safety requirements, and applicable codes before buying or building.
Reviewed September 6, 2026Runs in your browser
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How this calculator works
Square feet = length × width × quantity. Optional extra is added by multiplying by 1 + the waste percentage.
Worked example
Two 15 × 12 ft rooms total 360 square feet before any waste allowance.
Sources & assumptions
Each rectangle is length × width, multiplied by quantity and the optional waste allowance. Split irregular spaces into measurable sections and subtract excluded areas.
Frequently asked questions
How do I handle an irregular room?
Split it into rectangles, calculate each area, and add the results. Subtract areas that are not part of the project.
When should I add waste?
Material projects often need extra for cuts, breakage, matching, and future repairs. The suitable percentage varies by material and layout.