How do you calculate diameter of a circle if you have area of a circle?

Answer 1

Perhaps the easier way is to re-arrange the standard formula, A = pi.R^2 where A is area, R the radius

So A/pi = R^2

Then R = square-root (A/pi)

Then multiply R by 2 for the Diameter.

HOWEVER

A more direct alternative uses A = pi.R^2 therefore so A = (p/4).D^2 ; and a neat keyboard "trick" that makes this method easy to memorise.

Now, pi/4 = 0.7854, whose digits by happy coincidence live in the top-left corner of the standard (3 x 3) calculator keyboard.

So now D = square-root (A/0.7854)