# Annulus Calculator

An Annulus is an object in the form of a ring (the area between two concentric circles). In order to calculate the annulus, it is necessary to input the dimensions of the inner and outer circles.

The number of decimal places is preset to be 2.

The user of the Annulus Calculator is capable of controlling the number of decimal places, he/she wants to calculate to.

Annulus

Dimension Outer Inner Notes
Diameter D1 mm D2 mm D1(Outside diameter), D2(Inside diameter)
Radius r1 mm r2 mm The Radius is the distance from the circle's center to its edge
Circumference C1 mm C2 mm The Circumference is the distance around a circle
Area A1 sq.mm A2 sq.mm Area is π x Radius2
Area of Annulus (A0) sq.mm Calculated by subtracting the area of circle of r1 from the area of circle of r2.
Width W mm Calculated by dividing the difference between the outside diameter(D1) and inside diameter(D2) by two.

You may set the number of decimal places in the online calculator. By default there are only two decimal places.

### The following algorithms are included into the Annulus Calculator

Area of the annulus (A0) = A1 - A2

A0 = π x (r12 - r22)

Diameter is the Radius x 2

Radius is the Diameter x 0.5

Circumference is π x Diameter

π is 3.141592654 (to 9 decimal places)