The Radius is the distance from the center of the circle to the circumference. Radius = √(Area / π) ie. the square root of the area divided by PI.
The Diameter of a circle is the distance from one point of the circumference through the center to the opposite side of the circle. The diameter is twice the length of the radius.
The circumference of a circle is the circular line that marks the limits of a circle. It is 6.29 (2xPI) times the radius or 3.14 (22 / 7).
You can solve for three other components by typing in a number and press the opposite "Solve Others".