Enter the inside diameter and cross-sectional diameter into the calculator to determine the outside diameter of the O Ring. This calculator can also evaluate any of the variables given the others are known.

O Ring Size Formula

The following formula is used to calculate the O Ring size.

OD = ID + (2 * CS)

Variables:

  • OD is the outside diameter of the O Ring (mm) ID is the inside diameter of the O Ring (mm) CS is the cross-sectional diameter of the O Ring (mm)

To calculate the O Ring size, multiply the cross-sectional diameter by 2 and add the result to the inside diameter. This will give you the outside diameter of the O Ring.

What is an O Ring Size?

An O-ring size refers to the dimensions of an O-ring, a mechanical gasket in the shape of a torus or doughnut. The size is typically defined by its internal diameter (ID) and its cross-sectional diameter (CS). These dimensions are crucial in ensuring a proper fit and effective seal in a variety of applications, such as in mechanical devices and plumbing systems, to prevent the escape or entry of gases or fluids.

How to Calculate O Ring Size?

The following steps outline how to calculate the O Ring Size using the formula: OD = ID + (2 * CS).


  1. First, determine the inside diameter of the O Ring (ID) in millimeters (mm).
  2. Next, determine the cross-sectional diameter of the O Ring (CS) in millimeters (mm).
  3. Next, use the formula OD = ID + (2 * CS) to calculate the outside diameter of the O Ring (OD) in millimeters (mm).
  4. Finally, calculate the O Ring Size.
  5. After inserting the variables and calculating the result, check your answer with the appropriate measuring tools.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Inside diameter of the O Ring (ID) = 10 mm

Cross-sectional diameter of the O Ring (CS) = 5 mm