Circle Calculator - Calculate Circumference and Area

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

• 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

• 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