How to Solve for Radius in Excel. The radius of a circle or a sphere is the distance between the center and the edge. The radius can be used to calculate a circle's diameter, area and circumference.

To find the equation of a circle when you know the radius and centre, use the formula (x a) 2 + (y b) 2 = r 2, where (a, b) represents the centre of the circle, and r is the radius.