Area & Perimeter
Area drives most material takeoffs — flooring, paint, paving, and roofing all start here.
Rectangle: length × width · Triangle: ½ × base × height · Circle: π r² (circumference 2 π r) · Perimeter: 2 × (length + width) · square feet ÷ 9 = square yards.
Worked examples
- A 20 ft × 30 ft slab = 600 sq ft.
- A 9 ft × 12 ft floor = 108 sq ft = 12 sq yd (108 ÷ 9).
- A wall 8 ft × 25 ft = 200 sq ft; subtract a 3 ft × 7 ft door (21 sq ft) → 179 sq ft of paint.
- A 50 ft × 80 ft lot needs 260 ft of fence (perimeter).
Always subtract large openings (doors, windows) from a paint or covering estimate, and convert to the units the material is sold in (square yards, squares, etc.).
Practice: Area & Perimeter
Frequently asked
How do you convert square feet to square yards?
What is the area of a circle?
More Construction Math topics
Volume & Material Takeoff
Construction math: concrete cubic yards, the 27 cubic feet rule, one cubic yard covering 81 sq ft at 4 inches, asphalt tonnage, and excavation volume takeoffs.
Read & practice →Unit Conversions
Construction math conversions: square feet to square yards (÷9), cubic feet to cubic yards (÷27), inches to feet, acres, tons, gallons, and bags of concrete per cubic yard.
Read & practice →Percentages, Slope & Grade
Construction math: percent grade (rise over run), slope ratios, ADA 1:12 ramps and 2% cross slope, waste factors, and percent-of calculations.
Read & practice →Estimating & Costs
Construction math for estimating: labor cost, unit pricing, markup vs. margin, adding overhead and profit to a bid, crew production rates, and converting a labor budget to hours.
Read & practice →Geometry & Right Triangles
Construction math: the 3-4-5 rule for squaring layouts, the Pythagorean theorem for rafters and diagonals, roof pitch, and circle radius and diameter.
Read & practice →