How do I use the Circle Area Calculator?
Enter your values in the fields and the result updates instantly as you type.
Circle Area Calculator
Compute area and circumference of a circle from radius. Enter your values, review the formula, and use the worked result as a quick check for everyday planning.
Circle Area Calculator
Compute area and circumference of a circle from radius.
e.g., cm, m, ft, in
Results
Area
113.097336 sq units
Circumference
37.699112 units
Formula: Area = pi * r^2, Circumference = 2 * pi * r
Circle Area and Circumference from Radius
Calculate the area and circumference of a circle from its radius. Enter any radius value and get both results instantly using π (pi). Essential for geometry, construction, crafts, and engineering.
Formula
Area = π × r². Circumference = 2 × π × r. The calculator uses Math.PI for high precision. Area units are square of the input unit; circumference units are the same as the input unit.
Worked example
Radius 6 units: area = π × 36 = 113.097 sq units, circumference = 2π × 6 = 37.699 units.
Practical guidance
Using diameter instead of radius
If you have the diameter, divide by 2 to get the radius before entering. A circle with diameter 10 has radius 5. Area = π × 25 = 78.54. Circumference = π × 10 = 31.42 (or 2π × 5, same result).
Real-world applications
Calculate pizza area to compare sizes (12-inch vs 14-inch — area grows with square of radius). Determine circular garden bed soil volume (area × depth). Size round tables for events (diameter = 2 × radius).
Frequently asked questions
What formula does this calculator use?
Area = pi * r^2, Circumference = 2 * pi * r
Can I use decimal values?
Yes. Decimal inputs are supported for most calculators. Integer-based tools use rounded integer values where appropriate.
Is this calculator free?
Yes. CalcuNimble calculators are free and optimized for fast everyday use.