Area Calculator
Calculate the area of a rectangle, triangle, circle, trapezoid or ellipse from its dimensions.
How it works
Rectangle: l × w · Triangle: ½bh · Circle: πr² · Trapezoid: ½(a + b)h · Ellipse: πab
Each shape has its own area rule, but they’re related: a triangle is half a rectangle with the same base and height, and a trapezoid averages its two parallel sides before multiplying by the height between them. For the ellipse, a and b are the semi-axes — half the widest and half the narrowest span.
Worked example
A rectangle 8 units long and 5 units wide has area 8 × 5 = 40 square units. Switching to a trapezoid with parallel sides 8 and 5 and height 4: A = ½ × (8 + 5) × 4 = 26 square units.
Frequently asked questions
Which height does a triangle use?
The perpendicular height — straight from the base to the opposite corner at 90°, not along a slanted side. If you only know three side lengths, use the Triangle Area Calculator instead.
What counts as a and b on the trapezoid?
The two parallel sides (the slanted legs don’t enter the formula). The height is the perpendicular distance between those parallel sides.
How do I convert between square units?
Square the length conversion: 1 foot = 12 inches, so 1 square foot = 144 square inches, and 1 square meter ≈ 10.764 square feet.
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This calculator is for educational purposes. Double-check important results before acting on them.