Circle Calculator

Find a circle's area, circumference and diameter from its radius.

Area 78.54

Circumference 31.416

Diameter 10

Formula: area = π r² ; circumference = 2 π r

Step-by-step with your numbers:

1. Values used:

2. Radius = 5

4. Radius squared = 5 x 5 = 25

5. Area = pi x Radius squared = 3.142 x 25 = 78.54

6. Circumference = 31.416

7. Diameter = 10

Did we solve your problem today?

Enter a radius to get the circle's area, circumference and diameter instantly.

The math behind it

Area = π × radius². Circumference = 2 × π × radius. Diameter = 2 × radius.

Radius 5 → area = π × 25 = 78.54, circumference = 31.42.

What if I only know the diameter?

The radius is half the diameter — divide by 2 first.