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# Annulus Formula

This page offers you the list of inner and outer circle formulas to find the inner and outer circumference of an annulus, surface area of the space enclosed by the inner circle and outer circle and finally the surface area of the annulus. Just by knowing the radius value of the inner and outer circle, we can easily calculate the surface area and circumference values. Substitute the radius in this annulus formula to manually calculate the values.

# Inner and Outer Circle Formula

#### Formula:

i = 2 × π × r2
o = 2 × π × r1
a = π × r2 × r2
b = π × d × r1
s = π × ((r1 × r1)-( r2 × r2))

Where,

i = Inner Circumference of an Annulus
o = Outer Circumference of an Annulus
a = Surface Area of the Space Enclosed by the Inner Circle
b = Surface Area of the Space Enclosed by the Outer Circle
s = Surface Area of the Annulus
r2 = Radius of Inner Circle
r1= Radius of Outer Circle

#### Related Calculator:

The above annulus formula is based on the radius of the inner and outer circle. You can also use our online calculator given above to find the inner circumference, outer circumference and surface area within seconds.