How to Calculate Square Footage for Any Shape (Rectangle, Triangle, Circle, L-Shape)
Rectangles are easy. But what about L-shaped rooms, triangular yards, and circular patios? Here is how to calculate any shape without a geometry degree.
Square footage determines how much paint, flooring, carpet, mulch, sod, or gravel you need for a project. Get it wrong and you either run short (second delivery fee, project delay) or overbuy (money wasted, materials stored in your garage for years). The math is simple for each shape — the trick is recognizing which formula to use.
Rectangle: Length × Width
A 14-foot by 12-foot room is 168 square feet. This covers most rooms, driveways, and patios. Measure along the longest wall for length and the perpendicular wall for width. If walls are not perfectly straight (they rarely are in older homes), measure in 2-3 spots and use the average.
Triangle: Base × Height ÷ 2
A triangular garden bed with a 10-foot base and 6-foot height is 30 square feet. The "height" is the perpendicular distance from the base to the opposite point — not the length of either slanted side. For irregular triangles, you can always draw a rectangle around the triangle and calculate half its area.
Circle: π × Radius²
A circular patio with a 10-foot diameter has a 5-foot radius. Area = 3.14159 × 5² = 78.5 square feet. For semicircles (half-circle windows, bay areas), divide by 2: 39.25 square feet.
L-Shapes and Irregular Rooms
Break the L into two rectangles, calculate each separately, and add them. A room that is 20 feet long and 12 feet wide with a 6-foot by 8-foot nook: main area (20 × 12 = 240) plus nook (6 × 8 = 48) = 288 square feet. This "divide into simple shapes" method works for any irregular floor plan — break it into rectangles, triangles, and circles, calculate each piece, and sum the results.
Skip the math entirely with our square footage calculator — it handles rectangles, triangles, circles, and trapezoids with instant results.