Radius (R): Diameter (D): Circumference (C): Area (A):

Results:

Circle Formulas & Instructions

Key Formulas

Diameter (D): D = 2 × Radius
Circumference (C): C = 2π × Radius
Area (A): A = π × Radius²

How to Use:

Enter one known value for the circle (radius, diameter, circumference, or area) and press "Calculate". The calculator will compute the other values.

Helpful Tips:

For accurate results, ensure you enter values with proper units.
Clear all inputs using the "Reset" button before starting new calculations.

Circle Calculator: Compute Area, Circumference, and Diameter

Use our Circle Calculator to find the area, circumference, radius, or diameter of a circle. Just enter one known value, and the tool will do the rest for you instantly.

What Is a Circle?

A circle is a perfectly round shape in which every point on the edge is the same distance from the center. It’s defined by its radius (r), diameter (d), area (A), and circumference (C).

Circle Formulas:

Diameter (d) = 2 × radius
Circumference (C) = 2 × π × radius
Area (A) = π × radius²

How to Use the Circle Calculator

Enter one known value: radius, diameter, circumference, or area.
The calculator will compute the remaining measurements.
Results are updated instantly for easy reference.

Example:

If you enter a radius of 5 cm, the calculator will determine:

Diameter = 10 cm
Area = 78.54 cm²
Circumference = 31.42 cm

Why Use a Circle Calculator?

Whether you’re a student solving geometry problems, a designer working with circular elements, or a DIY enthusiast cutting round objects—this tool saves time and ensures accurate results.

Note:

All calculations use π ≈ 3.1416 by default.