How to calculate square footage
Measure each area in feet, calculate the correct shape, then add the sections together. Add material waste only after finding the actual project area.
15×12 ft room plus 12×10 ft room
300 ft² of measured floor area
The room calculation
The 30 extra square feet are a purchasing allowance, not part of the measured floor area.
Formulas for common shapes
| Shape | Area formula | Measurement note |
|---|---|---|
| Rectangle | length × width | Use perpendicular dimensions |
| Triangle | base × height ÷ 2 | Height is perpendicular to base |
| Circle | π × radius² | Radius is half the diameter |
| Trapezoid | (side A + side B) ÷ 2 × height | A and B are parallel sides |
Measure irregular spaces
- Sketch the space and divide it into simple shapes.
- Measure to a consistent precision and record units.
- Calculate each shape separately.
- Add included sections and subtract large exclusions.
- Keep the measured area separate from the purchase quantity.
Choose waste for the material
Flooring, tile, roofing, and sheet goods require extra material for cuts, layout, defects, breakage, and future repair. The percentage depends on product format, pattern, room shape, installation direction, and installer guidance. Paint coverage and bulk-material depth require different calculations, so use the matching calculator rather than applying a square-foot allowance alone.
Frequently asked questions
How do I convert inches to feet?
Divide inches by 12. For example, 6 inches equals 0.5 foot.
Should closets be included?
Include every surface receiving the material. Measure closets separately if that makes the layout easier to verify.
Is square footage the same as linear footage?
No. Square footage measures area; linear footage measures length. Trim, edging, and fencing are often purchased using linear feet.