Notes:

Area of the annulus between r1 and r2, the shaded area, is the area contained by the outer circle minus the area contained by the inner circle or a0 = a1 - a2.

You will need to know 2 items of information in order to calculate the remainder of variables. The following are the formulas we used in our calculations:

Given outer radius and inner radius of the annulus find the outer circumference, the inner circumference and the area of the shaded section of the annulus.

• c1 = 2 * Π * r1
• c2 = 2 * Π * r2
• a1 = Π * r1^2
• a2 = Π * r2^2
• a0 = a1 - a2

Given outer circumference and inner circumference of the annulus you can find the outer radius, the inner radius and the area of the shaded section of the annulus.

• r1 = c1 / (2 * Π )
• r2 = c2 / (2 * Π )
• a1 = Π * r1^2
• a2 = Π * r2^2
• a0 = a1 - a2

Given outer radius and inner circumference of the annulus find the outer circumference, the inner radius and the area of the shaded section of the annulus.

• c1 = 2 * Π * r1
• r2 = c2 / (2 * Π)
• a1 = Π * r1^2
• a2 = Π * r2^2
• a0 = a1 - a2

Given inner radius and outer circumference find the outer radius, inner circumference and the area af the shaded section of the annulus.

• c2 = 2 * Π * r2
• r1 = c1 / (2 * Π)
• a1 = Π * r1^2
• a2 = Π * r2^2
• a0 = a1 - a2

Given area of the shaded section and the outer radius find the inner radius, the outer circumference and the inner circumference of the annulus.

• c1 = 2 * Π * r1
• a1 = Π * r1^2
• a2 = a1 - a0
• r2 = square root (a2 / Π)
• c2 = 2 * Π * r2

Given area of the shaded section and the inner radius find the outer radius, the outer circumference and the inner circumference of the annulus.

• c2 = 2 * Π * r2
• a2 = Π * r2^2
• a1 = a0 + a2
• r1 = square root (a1 / Π)
• c1 = 2 * Π * r1

Given area of the shaded section and the outer circumference find the inner circumference, the outer radius and the inner radius of the annulus.

• r1 = c1 / (2 * Π)
• a1 = Π * r1^2
• a2 = a1 - a0
• r2 = square root (a2 / Π )
• c2 = 2 * Π* r2

Given area of the shaded section and the inner circumference find the outer circumference, the outer radius and the inner radius of the annulus.

• r2 = c2 / (2 * Π)
• a2 = Π * r2^2
• a1 = a0 + a2
• r1 = square root (a1 / Π )
• c1 = 2 * Π * r1

Free online calculator for an annulus