Square Footage Calculator
Calculate area for rectangles, triangles, circles and multi-room projects.
Total square footage
100 sq ft
- Area 1
- 100 sq ft
How we calculate this
Square footage is length × width for rectangles, base × height ÷ 2 for triangles, and π × radius² for circles. Add multiple areas together — one per room, wall, or section of your project — to get a project total.
Example
Measuring tips
Measure at the longest points of each wall, not along baseboards or trim. For irregular rooms, break the space into rectangles and triangles and add each area separately using the "Add Area" button above.
Common mistakes
- Measuring only one wall and assuming the room is a perfect square.
- Forgetting to subtract or separately account for closets and alcoves.
- Not adding a waste allowance for tile, flooring, or roofing materials that require cuts.
Frequently asked questions
How do I calculate square footage for an irregular room?
Split the room into rectangles, triangles, or circles that you can measure individually, add each one as a separate area above, and the calculator will sum the total.
Should I add a waste allowance?
Yes for materials sold in fixed units (tile, flooring, shingles) — 10% is a common starting point, more for diagonal patterns or complex cuts.
Does this calculator work for roofing?
Yes — measure each roof plane as a rectangle or triangle. For pitched roofs, use the actual sloped length, not the flat footprint.
Related calculators
Estimates are provided for planning purposes. Actual material requirements may vary based on supplier specifications, compaction, site conditions, installation method, waste, and local code.