Tag Archives: o-ring size

How to Properly Measure an O-Ring

Measuring an O-Ring is quite simple when you have the right tools at your disposal. All that is required is a clean, level surface; an o-ring; and a measuring device such as a caliper or other measuring tools such as cones, gauges, and size charts.

Directions to Measure an O-Ring

To measure an O-Ring, following the directions below:

  1. Place your o-ring on a flat surface clean of debris.
  2. Determine the inside diameter (ID) and outside diameter (OD) of the o-ring. The o-ring dimensions chart below illustrates where on the o-ring each dimension is measured.
  3. Measuring the width, or cross-section (CS), can be tricky and is measured by lightly pressing the caliper ends onto O-ring as shown in section A-A.

For more information on O-ring sizes click to see the JIS B 2401 Standard O-Ring Size Tables.

Dimensionally specifying an o-ring can typically be done with just two dimensions, the inner diameter (ID) and the cross-section (CS). Occasionally, an O-ring may be specified with an outer diameter (OD) and cross-section or an inner diameter and outer diameter. If two of the three dimensions are known, the third can be calculated using the formulas shown below.

O-Ring Dimensions

O-Ring Dimensions


O-Ring Dimension Calculations

o-ring dimension calculations

The original article can be found on Dichtomatik’s website. Gallagher Fluid Seals is a distributor of Dichtomatik, a brand of Freudenberg.

For more information about measuring o-rings or determining the best o-ring to use, please contact Gallagher’s engineering department.

A Guide to O-Ring Sizes

o-ring sizesO-Rings are solid-rubber, doughnut-shaped seals used to block the passage of a gas or liquid when pressed between two mating surfaces.

They are amongst the most widely utilized seal designs in the world. Due to the number of ways they can be utilized, there are essentially an endless number of O-Ring sizes.

But despite the wide range of O-Ring sizes, every O-Ring has the same two dimensions: the inner diameter (ID), and the cross-section (CS). To attain an adequate seal, it must achieve proper compression, approximately 18-20% in the cross sectional characteristic.  This creates a boundary to keep fluids in and contaminants out.

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