Calculate circumference and area from a circle radius.
Right triangles, areas, slopes, distances and common coordinate-geometry formulas.
Enter the requested values above and select Calculate. The result updates immediately on the page, so you can change one value and compare different scenarios without leaving the calculator.
A circle with radius 5 has circumference about 31.416 and area about 78.540 square units.
Calculate circumference and area from a circle radius. It is designed for quick estimates and everyday problem solving. When a calculation affects a contract, tax filing, medical decision or other high-stakes situation, verify the result with the appropriate professional or authoritative source.
For a circle of radius 7 cm, the diameter is 14 cm, circumference is 2π × 7 ≈ 43.98 cm, and area is π × 7² ≈ 153.94 cm².
Common error: using a diameter of 14 as the radius makes the reported area four times too large. Circumference is a length; area uses square units. These calculations assume a true circle.
Calculate circumference and area from a circle radius.
Circumference = 2πr. Area = πr².
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