Circumference of a circle

As seen in the number pi , the formula for the circumference of a circle is

C = 2 × pi × r

If r is known, simply substitute the known value for r in the formula. Use 3.14 for pi.

Examples:


1) Calculate C if r = 2 inches

C = 2 × pi × r = 2 × 3.14 × 2 = 12.56 inches

2) Calculate C if r = 4 inches

C = 2 × pi × r = 2 × 3.14 × 4 = 25.12 inches

3) If C = 50.24 inches, calculate r.

Review solving multiplication equations before looking at the solution below.