How to Accurately Size an O-Ring the First Time Around?

Silicon O Rings suppliers

How to Accurately Size an O-Ring the First Time Around?

What defines an O-ring is the colour, material, diameter, and size. Before you order from the O Ring supplier, you must determine these factors. In your case, you will apply the correct method that would help you choose the size you want. Doing this will save you additional costs and frustration. Continue reading to determine how to size an O-ring the first time around accurately.

How to Measure O-ring Cross-section and Inside Diameter

The best way to know the size of an O-ring is by measuring the inside diameter and the cross-section. You can use a tool like a micrometer to measure the cross-section. However, if you don’t have this tool, there are a lot of alternatives you can get in your local O Rings and seals suppliers.

The inside diameter can also be measured using the micrometer, but for the larger inside diameter, you will have to use tools like Pi-Tape or O-sizer. After you have measured the two-section, you can use the O-ring chart to determine the standard size corresponding to your 0-ring. Also, you can work hand in hand with the O Ring supplier to assist you in the process.

The Sizing Process Using the Dimension and Tolerance

Step 1: Determine if it falls under Metric or Standard O-ring Sizes 

You can describe the O-ring size using either metric using mm or standard using inches. Use it as your reference when the dimension you got matches the AS568 standard O-ring chart size. If the O-Ring does not match the standard size chart, you can use the metric size as your reference. 

One thing that you have to consider when sizing your O-Ring is the tolerances. Tolerance vary based on the dimensions, size, manufacture or Oil Seal suppliers. The variance in the dimension is referred to as the tolerances. The acceptable tolerance is specified on the AS568 O-ring size chart. Therefore based on the size of the O-Ring then the tolerance value will vary but not with a large value.

Step 2: Sizing based on the size chart

  • O-Ring Standard Sizes

The cross-section size of the standard series includes 0.070, 0.103, 0.139, 0.210, or 0.275 inches. If your measuring falls under this range, your O-Ring is a standard size. Then you will have to measure its inside diameter and compare it with the size on the chart. If you find that the inside diameter is on the chart or within the tolerance, you will get its standard size. You will have to look for the three digits dash, and these values will be your O-Ring standard size.

  • Metric O-Ring Sizes

For the metric sizes, you have to use it if you could not find the O-Ring size through the standard AS568 chart. Here you will measure the cross-section and the inner diameter to get the dimension to compare them with the metric chart. Here you will get the size by multiplying the cross-section and inner diameter size in the following format #. ## X ###. For example, if you have a 2 mm cross-section and 6 mm inner diameter, the size will be 2.00X006.


The above is the process you can follow to Accurately Size an O-Ring the First Time Around. Before you order from O Ring suppliers in Dubai or any place, you should determine the size you want. Remember, during the selection and sizing, you can follow the guide on the sizing process or reach out to the suppliers to help you.