Annulus Calculator

  • Enter the outer and inner radii for the annulus.
  • Select the unit for area and circumference calculation.
  • Click "Calculate" to calculate the attributes of the annulus.
  • View the results below, including detailed calculations.
  • Use the chart to visualize the annulus.
  • Copy the results or clear them as needed.
  • Check the calculation history for previous entries.
Calculation Details:

Area: The area of the annulus is calculated using the formula A = π(R2^2 - R1^2).

Inner Circumference: The inner circumference is calculated using the formula C = 2πR1.

Outer Circumference: The outer circumference is calculated using the formula C = 2πR2.

Inner Circle Area: The area of the inner circle is calculated using the formula A = πR1^2.

Outer Circle Area: The area of the outer circle is calculated using the formula A = πR2^2.

Calculation History:


    The Annulus Calculator is a valuable tool used to calculate various properties of an annulus, a geometric shape that resembles a ring or a circular doughnut. This tool is essential for engineers, mathematicians, and professionals working in various fields.

    Understanding the Annulus


    An annulus, also known as a ring, is a two-dimensional geometric shape formed by two concentric circles. It consists of an outer circle and an inner circle, and the region between these two circles is the annular region. The outer circle’s radius is denoted as “R,” and the inner circle’s radius is denoted as “r.” The distance between the two circles is called the width or the thickness of the annulus, which can be represented as “w.”


    Several formulae are associated with the annulus, which allows us to calculate various properties of this shape:

    Area of Annulus (A)

    The formula to calculate the area of an annulus is given by: A = π(R^2 – r^2)

    Perimeter of Annulus (P)

    The formula to calculate the perimeter (circumference) of an annulus is: P = 2π(R + r)

    Width of Annulus (w)

    The width or thickness of the annulus can be calculated as: w = R – r

    Outer Circumference (C1) and Inner Circumference (C2)

    The circumferences of the outer and inner circles can be calculated as: C1 = 2πR C2 = 2πr

    Example Calculations

    Let’s illustrate the use of the Annulus Calculator with a few examples:

    Example 1:

    Suppose you have an annulus with an outer radius (R) of 8 cm and an inner radius (r) of 5 cm. Calculate its area.

    Using the formula for the area of an annulus: A = π(R^2 – r^2) A = π(8^2 – 5^2) A = π(64 – 25) A = π(39) A ≈ 122.52 square centimeters

    Example 2:

    Given the same annulus as in Example 1, calculate its perimeter.

    Using the formula for the perimeter of an annulus: P = 2π(R + r) P = 2π(8 + 5) P = 2π(13) P ≈ 81.68 centimeters

    Real-World Use Cases

    The Annulus Calculator finds applications in various fields, including engineering, architecture, physics, and design. Here are some real-world use cases:

    Engineering and Architecture

    In civil engineering and architecture, annular structures such as retaining walls, water tanks, and arches are common. Engineers use the Annulus Calculator to determine the material requirements, load-bearing capacity, and structural integrity of these structures.


    In manufacturing, annular components like washers, gaskets, and bearings are crucial. The calculator helps manufacturers design and produce these components with precise dimensions and tolerances.


    Physicists use annuli to model various physical phenomena, such as the behavior of electromagnetic fields in coaxial cables or the flow of fluids in pipes with concentric cross-sections. The Annulus Calculator aids in solving mathematical models for these systems.

    Art and Design

    Artists and designers incorporate annular shapes in their creations. The calculator allows them to calculate proportions and dimensions accurately.


    The Annulus Calculator is a powerful tool for calculating the properties of annular shapes, providing invaluable assistance in a wide range of fields.

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