O-Ring Size Chart
Look up O-ring sizes by inside diameter and cross-section (AS568, JIS B 2401, ISO 3601)
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Finds the standard O-ring that matches a measured ring, and lists the AS568, JIS B 2401 and ISO 3601-1 size tables with inside diameter and cross-section. Use it to identify a worn O-ring or to translate a size name into dimensions.
How to use
- Under "Find the nearest standard size", choose whether you measured the inside or the outside diameter, enter it with the "Cross-section (CS)", and pick mm or in.
- Read the three closest sizes of each standard with the difference in inside diameter and cross-section.
- If you already have a size name such as P20, G25, -210 or B0250, type it under "Look up a size" to see its dimensions.
- Below, choose a standard and a cross-section to see the full table, and use "Print" for a paper copy.
How it works
- Outside diameter = inside diameter + 2 × cross-section; the page uses this to work from a measured outside diameter.
- Every size is listed only if at least two independent sources agree. AS568 tolerances are shown; JIS and ISO tolerances are left out because they could not be confirmed twice.
- JIS P sizes are for moving seals, G for fixed seals and V for vacuum flanges. ISO 3601-1 inch sizes use the AS568 numbers.
- Groove dimensions, pressure limits and materials are not covered.
Questions and answers
- What size is a JIS P20 O-ring?
- P20 has an inside diameter of 19.8 mm and a cross-section of 2.4 mm, so the outside diameter is about 24.6 mm.
- What are the dimensions of an AS568-210 O-ring?
- Inside diameter 0.734 ± 0.010 in (18.64 mm) and cross-section 0.139 ± 0.004 in (3.53 mm).
- How do I measure an old O-ring?
- Measure the cross-section in several places and the inside diameter without stretching the ring. Used rings are often flattened or stretched, so compare with the nearest standard values rather than expecting an exact match.
- What is the difference between JIS P and G O-rings?
- P sizes are made for moving parts and can also seal static joints; G sizes are for fixed joints. At the same nominal number they have different dimensions, for example P25 is 24.7 × 3.5 mm and G25 is 24.4 × 3.1 mm.