Circle Calculator
Calculate circle area, circumference, and diameter.
Circle Dimensions
Distance from center to edge
Circle Properties
Area
78.54
square units
Circumference
31.42
units
Diameter
10.00
units
Formulas:
Area = πr² = π × 5²
Circumference = 2πr = 2π × 5
Diameter = 2r = 2 × 5
About This Calculator
The Circle Calculator helps you calculate the area, circumference, and diameter of a circle from its radius. A circle is a perfectly round shape where all points are equidistant from the center.
Simply enter the radius of the circle, and the calculator will automatically compute the diameter (2 × radius), area (π × r²), and circumference (2 × π × r). All calculations use the mathematical constant π (pi), approximately 3.14159.
Formula & Calculation Method
Circle Formulas:
Diameter:
d = 2r
Area:
A = πr²
Circumference:
C = 2πr = πd
where:
r = radius
d = diameter
π ≈ 3.14159
The radius is the distance from the center to any point on the circle. The diameter is twice the radius. The area measures the space inside the circle, while the circumference measures the distance around the circle.
How to Use This Calculator
- Enter Radius: Input the radius of the circle.
- View Results: See the calculated diameter, area, and circumference.
- Use Results: All measurements use the same units as the radius.
Frequently Asked Questions
What is the difference between radius and diameter?
The radius is the distance from the center to the edge of the circle. The diameter is twice the radius - it's the distance across the circle through the center. Diameter = 2 × radius.
What is π (pi)?
Pi (π) is a mathematical constant approximately equal to 3.14159. It represents the ratio of a circle's circumference to its diameter. It's an irrational number with infinite decimal places.
How do I calculate circle area if I only know the circumference?
If you know the circumference (C), you can find the radius: r = C / (2π), then calculate area: A = πr². Or directly: A = C² / (4π).
What units are used?
The units depend on your radius input. If radius is in centimeters, area is in square centimeters and circumference is in centimeters. Ensure all measurements use consistent units.
Expert Reviewed
This calculator was reviewed by NumCalculators Editorial Team, Multi-disciplinary Expert Team