Circle Calculator

Calculate area, circumference, diameter, and radius of a circle easily.

Inputs

About Circle Geometry

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre.

Formulas Used

  • Circumference: C = 2πr = πd
  • Area: A = πr² = π(d/2)²
  • Diameter: d = 2r

Results

Embed This Calculator

laqayt logo

Share this tool with your audience. 100% free and fully responsive.

How Circle Calculator Works

Area = pi × r², Circumference = 2 × pi × r

Calculate all circle properties from any single known value - radius, diameter, circumference, or area. All values are mathematically related through pi.

  1. 1

    Step 1

    Select which value you know

  2. 2

    Step 2

    Enter the known measurement

  3. 3

    Step 3

    Click Calculate to see all circle properties

  4. 4

    Step 4

    View radius, diameter, circumference, and area

Use Cases

Calculating circular garden or pool dimensions

Engineering circular components

Finding wheel or tire measurements

Academic geometry problems

Tips

  • 1

    Pi (pi) is approximately 3.14159

  • 2

    The radius is always half the diameter

  • 3

    Circumference is also known as the perimeter or length of the circle

  • 4

    Area is proportional to the square of the radius

  • 5

    The diameter is the longest chord in the circle and passes through the center

Common Mistakes

  • Confusing radius with diameter in formulas

  • Forgetting to square the radius when calculating area

  • Using an inaccurate value for pi in precise calculations

  • Confusing length units with area units

Frequently Asked Questions

What is the difference between radius and diameter?
The radius is the distance from the center of the circle to its edge, while the diameter is the distance across the circle passing through the center. Diameter = 2 × radius.
Why do we use pi in circle calculations?
Pi is a constant ratio between any circle's circumference and its diameter. Its value is approximately 3.14159 and it is an irrational number.
How do I calculate the area of a semicircle?
Area of semicircle = (pi × r squared) / 2, which is half the area of the full circle.
What are the correct units for the results?
Radius, diameter, and circumference are in length units (meters, cm), while area is in square units (square meters, square cm).
How do I calculate the radius if I know the area?
Radius = sqrt(Area / pi). Take the square root of the area divided by pi.

Support Our Project

Our site is completely free, you can support us to help us stay online and develop new tools.

Buy me a coffee

Related Calculators

⭕

Circle Chord Calculator

Calculate circle chord length and distance from center.

⭕

Inscribed Circle Calculator

Calculate inscribed circle radius of a triangle.

⭕

Circumscribed Circle Calculator

Calculate circumscribed circle radius of a triangle.

📐

Triangle Calculator - Calculate Triangle Area and Properties

Calculate triangle properties including area, perimeter, angles, and sides. Free online triangle calculator for geometry problems. Solve any triangle with ease.

🔵

Sphere Calculator - Volume & Surface Area

Calculate sphere volume and surface area from radius.

📐

Cone Calculator - Volume & Surface Area

Calculate cone volume and surface area.