O-Ring Size Standards

An o-ring is one of the most common types of seals in the world. O-Rings are used in a variety of applications in different industries around the world. Because of its popularity, there is virtually an unlimited number of possible sizes of an o-ring. Thus, the need for size standards which cover the most common sizes used.

Over the years, many size standards have been developed for o-rings. The table below shows what we believe to be the most often used/referenced standards by our customers in the United States and other countries.

O-Ring Size Charts

**This information is only intended as a guide to identify o-ring sizes from the various international standards. Although we believe this information to be correct, we cannot guarantee 100% accuracy with each and every standard. Therefore, we recommend referral to the actual specifications before proceeding with design work, etc.**

International Size Charts PDF Guide

Need a handy reference to the different size standards? Check out our guide to International O-Ring Size Standards.


AS568 is the most commonly used standard in the United States for defining “inch sizes” of o-rings.

View Size Chart

BS 1806

British Standards Institution and lists all Imperial standard sizes. It has been superseded by BS ISO 3601.

BS 1806 Size Chart
View Size Chart

ISO 3601

International Organization for Standardization and contains both Class A and Class B O-Rings.

ISO 3601 Size Chart
View Size Chart

BS 4518

Issued by the British Standards Institution, Standard BS 4518 identifies British Standard metric sizes.

BS 4518 Size Chart
View Size Chart

SMS 1586

Swedish Mechanical Standard (Sveriges Mekanstandardisering). O-Rings are identified by ID and C/S.

SMS 1586 Size Chart
View Size Chart

DIN 3771

The German Institute for Standards (Duetsches Institut für Normung). O-Ring sizes shown as ID x C/S.

DIN 3771 Size Chart
View Size Chart

NF T 47-501

Association Française de Normalisation (French Standards Institute). Similar to ISO 3601-1.

NF T 47-501 Size Chart
View Size Chart

JIS B 2401

Japanese Industrial Standard for o-ring sizes. This standard, often referred to as “Japanese Metrics.”

JIS B 2401 Size Chart
View Size Chart

IS0 6149

ISO 6149 specifies o-rings designed for use in Metric Tube Fittings. Includes 13 different sizes and calls out the metric thread size for each o-ring size.

IS0 6149 Size Chart
View Size Chart

Generic Metric O-Ring Sizes

Included are the most common metric sizes matching up with any corresponding international standard sizes.

Generic Metric O-Ring Sizes
View Size Chart

Metric O-Ring Size Cross Reference Table

Common international size standards and allows cross-referencing to other standards.

Metric O-Ring Size Cross Reference Table
View Cross Reference Table

Parker 500 Series O-Ring Sizes

5-XXX sizes are o-rings of nonstandard dimensions for which Parker has tooling.

Parker© Series 5-XXX O-Ring Sizes
View Size Chart

Get The International O-Ring Size Standards Guide Emailed To You!


Some of the standards referenced here specify the acceptable tolerance ranges for the o-rings within that standard. However, With the exception of our AS568 Size Chart, our other size reference charts do not list tolerances, as these tend to vary between the standards issuing organizations. To view the size tolerances for the o-rings we sell, please refer to either the AS568 Size Chart for American Standard Sizes, or our Metric O-Ring Tolerances page for all other “metric” o-rings.