How do you calculate the radius of a circle?

Radius of a circle is half the diameter.

For any given circle draw a straight line from one point on the circulference, through the circle centre, to the opposite point on the circu,afenrece.

Then taking a rule measure the straight line distance. That is the diameter(d)

Half of this distance, that from the circle dentre to the circumference is the radius(r).

r + r = d

or

2r = d

or

r = d/2

From this straight line we can calculate both the area (A)and the circuference(C) by using the following eq'ns/

C = 2pir = pi*d

A = pi *r^(2)

'pi' is a constant for all circles. and the number 3.14 or 3.1416 or 22/7 are used in these APPROXIMATIONS.