When to use this calculator
Calculate the area enclosed by a circle from its radius. The radius runs from the centre to the circumference.
Explore the circle & ellipse calculators for other questions in this topic. For a related calculation, use the Circle Circumference Calculator: Find the distance around a circle using its radius.
PUTTING IT INTO PRACTICE
Circle Area: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Radius | 5 |
| Result | 78.539816 square units |
- Check the input labels and enter the example values above.
- Apply the relationship: Area = πr².
- The result is 78.539816 square units, rounded for display.
How to interpret your result
The radius runs from the centre to the circumference.
Distinguish radius from diameter before entering measurements. Arc length follows the curve, while chord length runs straight between endpoints. Ring-shaped areas subtract the inner circle from the outer one.
Frequently asked questions
How is chord length different from arc length?
A chord is a straight line between two points on the circle. An arc follows the circular boundary between those points.
How do I use the circle area calculator?
Enter radius. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Area = πr².
What should I check before using the result?
The radius runs from the centre to the circumference.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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