# Annulus Formula

The dimensions of an annulus are defined by the two radii R, r, which are the radii of the outer ring and the inner ‘hole’ respectively. The area of a circular ring can be found by subtraction the area of small circle from that of the large circle.

Here are formulas to find Area of Annulus

Where,

**A** = Area of Annulus

**R** = Outer radius

**r** = Inner radius

**(Pi) $\pi$** = is approximately 3.142

**Example 1:
**Find the area of the path, where a path is 14cm wide, surrounds a circular lawn whose diameter is 360cm.

**Solution:**

Given

Diameter of inner circle is 360cm, means the radius (r) is 180cm

Radius of outer circle is (R) = 180 + 14 = 194cm

A = $\pi$ ($R^{2}$ – $r^{2}$)

= 3.142 ($R^{2}$ + $r^{2}$) ($R^{2}$ – $r^{2}$)

= 3.142 (194 + 180) (194 – 180)

= 3.142 $\times$ 374 $\times$ 14

= 16451 cm^{2}