Circle Calculator
Calculate circumference, area, and diameter from radius. Simple geometry calculator.
How to Use
Enter your values in the fields above and click Calculate to get instant results. All computations run locally in your browser. No data is ever uploaded or stored.
Related Calculators
Circle Geometry and Calculations
CalcSolver's circle calculator computes all properties — area, circumference, diameter, and radius — from any single known value. The fundamental relationships: Area = πr², Circumference = 2πr, Diameter = 2r.
A circle with radius 5cm has area = 78.54 cm², circumference = 31.42 cm, and diameter = 10 cm. π ≈ 3.14159 appears in every circle calculation because it represents the constant ratio of circumference to diameter — a mathematical truth independent of circle size.
Circle calculations appear in engineering (pipe cross-sections for flow rate), construction (circular patios and columns), and manufacturing (drilling and cutting circles). Arc length and sector area require additional angle input. Use CalcSolver's triangle calculator for polygon geometry and scientific calculator for π-based computations.
Sponsored Content
The following content is provided by an ad partner and does not affect the calculator experience.
Frequently Asked Questions
How do you calculate the area of a circle?
The area of a circle is calculated using A = πr², where r is the radius. If you know the diameter, r = diameter ÷ 2. For example, a circle with radius 5 has area = π × 25 = 78.54 square units.
How do you calculate the circumference?
The circumference (perimeter) is C = 2πr or C = πd, where r is radius and d is diameter. A circle with diameter 10 has circumference = π × 10 = 31.42 units.
What is the relationship between diameter and radius?
The diameter is exactly twice the radius (d = 2r). The radius is the distance from the center to any point on the circle, while the diameter passes through the center connecting two points on the circle.