Home & Construction Calculators
Use this square footage calculator to estimate room, floor, wall, roof, garden, and project area with shape calculations, unit conversions, waste allowance, packages, and material cost.
About the Square Footage Calculator
This square footage calculator estimates area for rectangles, squares, circles, triangles, and trapezoids. It converts entered dimensions to square feet, applies identical-area quantity and waste, then estimates whole packages and material cost.
Core formulas
Rectangle = length × width. Square = side². Circle = π × radius². Triangle = ½ × base × height. Trapezoid = ½ × (parallel side A + parallel side B) × height. Adjusted area = area × quantity × (1 + waste ÷ 100).
Worked example
A rectangular room measuring 20 ft × 12 ft has 240 ft². With 10% waste, the adjusted area is 264 ft². If one package covers 32 ft², round up to 9 packages. At $28 per package, the estimated material cost is $252.
Measurement checklist
- Measure each floor, wall, roof, or garden section separately.
- Use one unit consistently for every dimension.
- Subtract permanent openings when appropriate.
- Use actual supplier package coverage.
- Add extra waste for diagonal patterns, curves, or many cuts.
Unit conversion guide
- 1 yd² = 9 ft²
- 1 m² = 10.7639 ft²
- 1 ft² = 144 in²
- 1 cm² = 0.00107639 ft²
- 1 acre = 43,560 ft²
Common mistakes
- Using diameter where radius is required.
- Mixing feet and inches without conversion.
- Rounding before applying waste.
- Rounding packages down.
- Confusing square feet with cubic feet.
Frequently asked questions
How do I calculate an L-shaped room?
Divide it into rectangles, calculate each rectangle, and add the results. Subtract any excluded openings.
How much waste should I add?
Simple layouts often need 5–10%. Diagonal patterns, curves, and irregular spaces may need more.
Is square footage the same as linear feet?
No. Square footage measures area, while linear feet measure one-dimensional length.
Can I use different measurement units?
Choose one unit for all dimensions. The calculator converts the resulting area to square feet.