Formulas
Rectangle = length × width Circle = 3.1416 × (diameter ÷ 2)² Triangle = ½ × base × height Half circle = circle ÷ 2
L-shapes and odd rooms
Split an L-shaped space into two rectangles that don't overlap, and add both. For a half-round bed or bay, add a half circle and measure its straight side. Being within a few percent is fine for buying materials, because your extra allowance covers the rest.
Common questions
How do I calculate square footage?
For a rectangle, multiply length × width in feet. For a circle, use π × radius². For a triangle, use ½ × base × height. Split odd shapes into these pieces and add them together.
How do I convert square inches to square feet?
Divide by 144. There are 12 × 12 = 144 square inches in a square foot.
How do I convert square meters to square feet?
Multiply by 10.764.
How many square feet are in a square yard?
Nine (3 ft × 3 ft).