Choose a shape and enter its dimensions to calculate the area.

How to Use the Area Calculator

Pick a shape first — the fields underneath change to match, since a circle needs a radius and a rectangle needs two sides.

Rectangle: length × width
Square:    side²
Triangle:  ½ × base × height
Circle:    π × radius²
Trapezoid: ½ × (base A + base B) × height

Five shapes, five formulas — this Area Calculator covers the ones that come up constantly: rectangle, square, triangle, circle, trapezoid. The ½ in the triangle formula isn't decorative: a triangle is exactly half of the parallelogram you'd get by duplicating it and rotating the copy 180°, and that parallelogram's area is plain base × height. Trapezoid does the same trick with two different-length parallel sides — average them first, then multiply by height, and you're really just applying the same base-times-height idea to an asymmetric shape.

π shows up in the circle formula because it's the fixed ratio between any circle's circumference and its diameter — the same constant, no matter the circle's size — and that relationship carries straight through into area.