Square footage formulas
Rectangle or square
Length × width. A 12 ft × 10 ft room is 120 sq ft.
Triangle
Base × perpendicular height ÷ 2. A triangle with a 10 ft base and 6 ft height is 30 sq ft.
Circle
π × radius². A circle with a 5 ft radius is about 78.54 sq ft.
L-shaped or irregular room
Split the space into rectangles or other simple shapes. Calculate each section separately, then add the results. Avoid using the maximum overall length × maximum overall width because that counts space outside the actual room.