Mathematics · Geometry
Circle Calculator
Calculate a circle's diameter, circumference and area from its radius.
Inputs and results stay in this browser. Change one value at a time to explore the relationship.
Calculation steps
- Diameter = 2 × 5 = 10.
- Circumference = 2π × 5 = 31.41592653589793.
- Area = π × 5² = 78.53981633974483.
Definition and formula
The radius controls every circle measure: length measures scale with r and area scales with r squared.
Diameter = 2r; circumference = 2πr; area = πr²
Worked example
For radius 5, diameter = 10, circumference ≈ 31.42 and area ≈ 78.54.
Common mistake
Area uses the radius squared; circumference does not.
How to learn with this calculator
Begin with the worked example, then change one value while keeping the others fixed. Compare the new result and calculation steps to identify which part of the formula changed.
Clear answers
Frequently asked questions
What does the Circle do?
Calculate a circle's diameter, circumference and area from its radius.
How does the Circle work?
The calculator applies Diameter = 2r; circumference = 2πr; area = πr². The radius controls every circle measure: length measures scale with r and area scales with r squared.
What can I learn from the Circle?
It connects the mathematical rule to your chosen numbers and shows each calculation step. Change one input at a time to see how the result responds.
Does MW SysArc receive or store what I enter?
No. The calculation runs locally in your browser. MW SysArc does not receive or store your calculation inputs.
How should I use the result?
Use the steps to understand the method, then verify important school or professional work using the notation and rounding rules required in your setting.
Last reviewed 2026-07-14. Calculations tested 2026-07-14.