Calculate the area of seven common shapes — rectangle, triangle, trapezoid, circle, sector, ellipse, or parallelogram.
Rectangle and parallelogram both boil down to base × height. Triangle uses Heron's formula (no angle needed, just three side lengths). Trapezoid averages its two parallel bases, multiplied by height. Circle, sector, and ellipse all trace back to π — a sector is just a circle's area scaled by what fraction of the full 360° it spans, and an ellipse is a circle stretched along two different radii.
Most irregular shapes can be estimated by splitting them into a combination of these simple shapes, calculating each piece's area separately, and adding them together — the same way an L-shaped room can be measured as two rectangles.
They're the longest and shortest radii of an ellipse, measured from its center. When they're equal, the ellipse is just a circle — that's why the circle formula (πr²) is a special case of the ellipse formula (πab).
A sector's area is the fraction of the full circle it covers — that fraction is angle÷360 in degrees, or angle÷2π in radians. Make sure to pick the matching unit for whatever angle you enter.
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