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Area of a Circle Calculator.

Calculate area and circumference from a circle radius.

On-device calculationNo signup
01

Set your values

Results update as you type.

Area: 78.539816 units²

Area

78.539816units²
Circumference: 31.415927 units

Circumference

31.415927units

Results update automatically as you type.

Use Cases

School Math Homework

Quickly verify area and circumference calculations for geometry assignments or exam practice.

Example: Find the area of a circle with radius 7 cm.

DIY and Craft Projects

Determine the amount of material needed for circular projects like tablecloths, rugs, or garden beds.

Example: Calculate the area of a circular garden bed with a radius of 3 meters.

Frequently Asked Questions

How do I calculate the area of a circle using this calculator?
Enter the circle's radius in the 'Radius' field. The calculator uses the formula A = π × r² to compute the area and also provides the circumference using C = 2 × π × r.
What units does the calculator use for the radius?
The calculator accepts any unit you enter for the radius (e.g., cm, m, inches). The area and circumference will be in the corresponding squared and linear units respectively.
Can I use this calculator if I only know the diameter?
Yes, simply divide the diameter by 2 to get the radius, then enter that value in the 'Radius' field. The calculator will then compute the area and circumference.

Tips & Common Mistakes

Tips

  • Ensure the radius is measured from the center to the edge of the circle, not the diameter.
  • Use consistent units for the radius to get the area in the correct squared units (e.g., cm², m²).
  • For quick estimates, you can use 3.14 for π, but the calculator uses a more precise value for accuracy.
  • Double-check your radius value before calculating, especially if you derived it from a diameter or circumference.

Common Mistakes to Avoid

  • Entering the diameter instead of the radius, which will give an area four times larger than correct.
  • Using different units for the radius and expecting the area in a specific unit without conversion.
  • Forgetting that the area is in square units, not linear units, which can lead to misinterpretation.

Last updated: August 13, 2026