You would multiply the diameter by the value of pi which is 3.14159.

You would take pi x 2 x diameter, since diameter is used to measure meters. The problem written out would be like this. 3.14 x 2 x 20 = 125.60.

The formula for circumference of a circle is 2 x pi x r

where pi = 22/7 = 3.14 and r = radius of the circle.

In this case if d=20, then r = d/2 = 10

thus, circumference of the circle = 2 x pi x r = 2 x 3.14 x 10 = 62.8m

where pi = 22/7 = 3.14 and r = radius of the circle.

In this case if d=20, then r = d/2 = 10

thus, circumference of the circle = 2 x pi x r = 2 x 3.14 x 10 = 62.8m