A flat shape which involves two circles similar to a ring is called as an annulus. The extent of the annulus in a plane is the area of the annulus which is calculated by the inner and outer circle radius. The given below is the annulus area formula to calculate the annular area on your own. As per the formula, reducing the squared radius of the inner circle from the squared radius of the outer circle and multiplying the resultant value with the value of π will give the annular area.
The above annulus area formula section provides you a annular diagram with which you can differentiate and understand the radius of inner circle and outer circle. Instead of π you can use the value 3.14159 in the formula for the calculation.