Enter a non-negative radius.
Geometry Calculator
Circle Calculator
Calculate diameter, circumference, area, semicircle area, and arc-related reference values from a radius.
Instant answer
Formula breakdown
Browser-based
Mobile friendly
Interactive calculator
Enter your values
Use the example values or replace them with your own. Required validation happens before the calculation.
Ready
Calculated answer
Result
Simple workflow
How to use the Circle Calculator
Follow these steps to get a reliable result and understand how it was produced.
Use 2r for diameter and 2πr for circumference.
Use πr² for area.
Understanding the calculation
Every circle measurement can be derived from the radius. The calculator uses JavaScript’s high-precision value of π.
Area A=πr²; circumference C=2πrThe result panel substitutes your numbers into this relationship and shows the important intermediate values.
Common uses
- Circular material estimates
- Geometry homework
- Diameter and circumference checks
Accuracy tips
- Area is in square units.
- Circumference and diameter are in linear units.
- A radius of zero represents a degenerate circle.
Helpful answers
Circle Calculator FAQs
Important details about formulas, inputs, limitations, and result interpretation.
What is the relationship between radius and diameter?
Diameter is twice the radius.
What value of π is used?
The calculator uses the browser’s Math.PI constant.
Can I enter a diameter instead?
Divide the diameter by two and enter the resulting radius.
Why is area squared but circumference is not?
Area measures a two-dimensional region, while circumference measures a one-dimensional boundary length.