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Square Footage
Calculator
Calculate square footage for 9 shapes, add multiple rooms to get total area, and estimate material costs for flooring, painting, carpet, and tile.
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How to Calculate Square Footage
Square footage is the area of a space measured in square feet. For a rectangle, multiply length × width. For other shapes, use the shape-specific formula below. Convert inches to feet first by dividing by 12.
All Square Footage Formulas
Rectangle: Area = Length × Width
Border/Frame: Area = (Outer L × Outer W) − (Inner L × Inner W)
Circle: Area = π × Radius²
Triangle: Area = ½ × Base × Height
Trapezoid: Area = ½ × (Base1 + Base2) × Height
Pentagon: Area = (s² × √(25+10√5)) / 4 ≈ 1.720 × s²
Hexagon: Area = (3√3 / 2) × s² ≈ 2.598 × s²
Octagon: Area = 2(1+√2) × s² ≈ 4.828 × s²
Sector: Area = (θ/360) × π × r²
1 sq ft = 0.0929 sq meters
1 sq meter = 10.764 sq feet
1 sq yard = 9 sq feet
How do I measure square footage of a room?
For a rectangular room: measure length and width in feet (use a tape measure). Multiply: Area = Length × Width. A 12×15 room = 180 sq ft. For an L-shaped room, split it into 2 rectangles, calculate each, then add. For irregular rooms, take the overall bounding box area and subtract the missing sections. Always add 10% to material orders to account for waste, cuts, and pattern matching.
How many square feet in an acre?
1 acre = 43,560 square feet. A standard American football field (including end zones) is about 1.32 acres or 57,600 sq ft. A typical suburban lot is 0.25 acres (about 10,890 sq ft). A city block is roughly 2–5 acres depending on the city. 1 hectare (metric) = 2.471 acres = 107,639 sq ft.
How do I calculate paint needed for a room?
Measure wall area: (perimeter × wall height) − (door and window area). Standard door = 20 sq ft, standard window = 15 sq ft. One gallon of paint covers ~350–400 sq ft for one coat. For two coats, divide total sq ft by 175–200. Example: 12×15 room, 8 ft ceilings, 2 doors, 2 windows. Perimeter = 54 ft. Wall area = 54×8 = 432 sq ft − 40 (doors) − 30 (windows) = 362 sq ft per coat. Two coats: ~724 sq ft → about 2 gallons.
How much flooring do I need for 1,000 sq ft?
Always add 10% for waste (cuts, defects, pattern matching). For diagonal installation, add 15%. So 1,000 sq ft needs 1,100 sq ft of material for standard installation, or 1,150 for diagonal. When buying in boxes, note the coverage per box (usually listed on box). If each box covers 20 sq ft, you need 1,100/20 = 55 boxes. Some installers recommend 5% overage for simple rooms, up to 20% for complex layouts or stone tile.