Math calculator
Circle Calculator
Calculate circle area, circumference, and diameter from radius.
Formula
Circle formulas
Area = pi r^2; circumference = 2 pi r; diameter = 2r
A radius of 5 gives area about 78.54.
FAQs
What unit is the area in?+
Area is in square units matching the radius unit.
Can I enter diameter?+
Enter half the diameter as the radius.
How does the Circle Calculator calculate the result?+
It uses the Circle formulas: Area = pi r^2; circumference = 2 pi r; diameter = 2r. A radius of 5 gives area about 78.54.
What information do I need to use the Circle Calculator?+
Calculate circle area, circumference, and diameter from radius.
How accurate is the Circle Calculator?+
Circle Calculator applies the formula and assumptions shown on this page. Results may be rounded for readability, so verify changing rates, thresholds, medical guidance, or legal rules with the cited source or a qualified professional.
What should I check before using the Circle Calculator result?+
Check that the units, dates, rates, and assumptions match your situation. Change one input at a time to understand which values have the largest effect on the result.
Math guide
How to use the Circle Calculator
Calculate circle area, circumference, and diameter from radius. The page also explains the circle formulas and shows a practical example: A radius of 5 gives area about 78.54.
- 1
Enter your details
Enter radius, then complete any other fields shown in the calculator.
- 2
Check the calculation
Review the result alongside the circle formulas: Area = pi r^2; circumference = 2 pi r; diameter = 2r.
- 3
Compare scenarios
Change one or more inputs to see how they affect the circle Calculator result before you use the estimate.
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