There are two main o-ring sizing types: standard and metric. Standard was developed for use in the United States, while the international community uses metric sizes. The metric sizes are further broken down by region, notably Europe and Japan.
Learn more about O-Ring sizes with the links below.
Seal & Design has all these sizes and more. We can provide virtually any required size.
Standard Sizes (AS568B)
The standard sizes used by O-ring manufacturers in the United States are defined by Aerospace Standard AS568B, Aerospace Size Standard for O-rings. That document, published by the Society of Automotive Engineers (SAE), lists the sizes of O-rings in six series or groups in both inches and millimeters. The first five series are based on cross-sectional diameter. The sixth series includes 20 sizes for boss seals. The standard sizes are also used for most military specifications.
Cross-sectional diameters range from 0.040 to 0.275 inch. Inside diameters range from 0.029 to 25.940 inches. There are 369 standard sizes.
Standard metric sizes for O-rings are defined by International Standard ISO 3601-1:2002: Fluid power systems O-rings Part 1: Inside diameters, cross-sections, tolerances and size identification code. That standard groups metric sizes into two series, G and A. The G series is used for general purpose applications and includes a wide range of inside diameters. The A series is used for aerospace applications where tighter tolerances are recommended. The G series has 445 sizes and the the A series has 383 sizes.
Currently, ISO sizes do not use a dash numbering system like the Aerospace Standard. ISO cross-sectional diameters differ from the Aerospace Standard by less than 0.001 inch. Therefore, many AS568B sizes are interchangeable with an ISO size. Be sure to consult ISO 3601-1 for specific dimensions, as inside diameters may differ.