Area Calculator
Calculate the area of common shapes.
Area
Use the same length unit for every dimension. Output is in square units.
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How this calculator works
Choose the shape before entering dimensions. A circle uses its radius, not its diameter. For a triangle, the height must be perpendicular to the base. For a trapezoid, enter the two parallel sides and their perpendicular separation. Keep all lengths in the same units before calculating square units.
Formula
rectangle = ab; triangle = ab/2; circle = πa²; trapezoid = (a+b)h/2
Assumptions & limitations
Use the same length unit for every dimension. Output is in square units.
Worked example
A rectangle 5 × 4 has area 20 square units.
To measure the space inside a solid rather than a flat surface, use the Volume Calculator and enter internal dimensions for capacity.
Our approach to calculations ↗Common questions
Should I enter radius or diameter for a circle?
Enter the radius, which is half the diameter. Using diameter as radius makes area four times too large.
Which triangle height should I use?
The perpendicular distance to the chosen base, not an arbitrary sloping side.
What are the trapezoid dimensions?
Enter the two parallel sides and their perpendicular separation. All dimensions must use the same length unit.