What is the formula for finding the circumference of a circle when you have the area?

The formula for the area of a circle is given by pi times radius times radius.

The formula for circumference of a circle is 2 times pi times radius.

As area is known, the radius is easy to work out, like this

From Area = pi X r X r

then

radius = (square root of (area/ pi))

From circumference = 2 X pi X radius

then

Circumference = 2 X pi X (square root of (area/pi))

This can be simplified to

Circumference = 2 sqrt(pi X area)

You will remember that pi stands for an endless decimal ratio that starts 3.142...

1. Divide the area by pi.
2. Get the square root of the answer. That's the radius.
3. Double it. That's the diameter.
4. Multiply the diameter by pi. That's the circumference.