O-Ring Size Chart & Standards Reference
Find the right size across AS568, ISO 3601, JIS B2401, DIN 3771 and metric general standards.
Choosing the correct O-ring size is critical for reliable sealing. Our size chart library covers the five most commonly used international standards, with full cross-reference tables, search-by-dimension tools, and downloadable PDFs for engineering documentation. O-ring sizing is not merely a matter of finding a part number. The interaction between inside diameter, cross-section, groove dimensions, and compression rate determines whether a seal will perform reliably or fail prematurely. Our size chart pages go beyond simple dimension tables to include tolerance classes, recommended groove geometries, and compression rate guidance for each standard. This contextual information helps you specify not just a size, but a complete sealing system. Different industries and regions favor different standards. North American aerospace, automotive, and hydraulic equipment traditionally uses AS568 dash numbers. European machinery and process equipment typically references ISO 3601 or DIN 3771 metric sizes. Japanese automotive and industrial equipment follows JIS B 2401. Understanding which standard your equipment was designed around is the first step in selecting the correct replacement or specifying a new seal. Our online tools complement the static size charts. The Size Converter instantly translates between AS568 dash numbers and metric millimeter dimensions, eliminating manual calculation errors. The Compression Calculator validates that your chosen size will achieve the optimal squeeze percentage in your groove. The Material Selector cross-references your size with compatible materials for your temperature and chemical environment. Together, these tools form an integrated specification workflow that reduces engineering time and specification risk. For maintenance teams, the size charts serve as a quick-reference field guide. When a seal fails and the part number has worn off or was never recorded, measuring the groove and using our metric search tool can identify the closest standard size within seconds. This capability is especially valuable for imported machinery where original documentation may be in a language or standard unfamiliar to your maintenance staff. All size chart data is available as free downloadable PDFs suitable for printing, binding, and inclusion in engineering manuals. The PDFs include both metric and imperial dimensions, tolerance tables per the relevant standard, and material recommendations. We update these charts annually to reflect any revisions to the underlying standards.
AS568
Aerospace Standard 568 (Imperial)
The most widely used imperial O-ring standard in North America. Covers 349 dash numbers from -001 to -475 with inch-based inside diameters and cross-sections.
ISO 3601
ISO 3601-1 (Metric O-Rings)
The global metric standard for O-ring sizes. Organized by inside diameter and cross-section in millimeters. Fully compatible with DIN 3771.
JIS B 2401
Japanese Industrial Standard B 2401
The primary O-ring standard for Japanese machinery and automotive applications. Covers P-series, G-series, S-series and V-series sizes.
DIN 3771
DIN 3771 Metric O-Rings
The German metric standard, functionally aligned with ISO 3601. Widely used in European hydraulic and pneumatic equipment.
BS 4518
British Standard 4518
The established British metric O-ring reference for engineering, maintenance and European procurement teams.
Metric General
General Metric O-Ring Sizes
Non-standard metric sizes commonly used in Asian manufacturing. Available by ID x CS in millimeters with no dash number system.
SMS 1588
Swedish Standard SMS 1588
A Scandinavian sizing reference used in hygienic process equipment, marine systems and Nordic supply chains.
NF T47-501
French Standard NF T47-501
A French metric standard commonly referenced in hydraulic, industrial and automotive sealing applications.
JASO F404
Japanese Automotive Standard JASO F404
An automotive-focused O-ring reference for fuel, oil, coolant and air-conditioning sealing in JDM and global vehicle platforms.
Engineering Tools
Size Converter
Convert between AS568 dash numbers and metric millimeter dimensions instantly.
Open ToolCompression Calculator
Calculate optimal squeeze percentage and gland fill ratio for any size.
Open ToolMaterial Selector
Match your size selection with the right material for temperature and chemical compatibility.
Open ToolFrequently Asked Questions
What is the most common O-ring size standard?
AS568 is the most common standard in North America and globally for inch-based equipment. ISO 3601 is the dominant metric standard in Europe and Asia. JIS B 2401 is prevalent in Japanese automotive and industrial equipment.
Can I interchange AS568 and ISO 3601 sizes?
Some sizes are dimensionally close but not identical. Always verify the actual ID and CS dimensions before substituting one standard for another. Use our Size Converter tool for exact comparisons. Interchanging standards without verification can lead to incorrect compression rates and seal failure.
Do you stock all standard sizes?
We carry the full AS568 range and the most commonly used ISO 3601 and JIS B 2401 sizes in NBR, FKM and EPDM from stock. Non-stock sizes are available on 7-15 day lead times. If you have a recurring requirement for a non-stock size, we can add it to our safety stock program.
Can you supply custom non-standard sizes?
Yes. We manufacture custom O-rings to any ID and cross-section dimension. MOQ starts at 1 piece for standard profiles. No tooling is required for cut/vulcanized cord or small-run molding. Custom molded parts with special profiles can be produced in 7-15 days with in-house tooling.
How do I measure an O-ring if the part number is worn off?
Use a digital caliper to measure the inside diameter (ID) and cross-section (CS) at multiple points. Enter these dimensions into our online Size Converter tool, which will identify the closest standard size across AS568, ISO 3601, and JIS B 2401. If no standard size matches, the seal may be custom. Send us the measurements and we will identify or reproduce it.
What tolerance should I specify for an O-ring?
Standard molded O-rings are typically manufactured to ISO 3601-1 Class B or AS568 standard tolerances. For precision applications such as medical devices or aerospace, Class A or customer-specific tolerances can be achieved. Tighter tolerances increase cost and may require specialized tooling. We recommend Class B for general industrial applications.
Can I download the size charts as Excel files?
Yes. Contact us and we will provide the size chart data in Excel or CSV format for import into your CAD, ERP, or inventory management system. This service is free for registered customers and distributors.
What is the difference between a standard size and a general metric size?
Standard sizes belong to an organized numbering system such as AS568 or ISO 3601 with defined tolerances and groove recommendations. General metric sizes are specified simply by ID x CS in millimeters without a dash number. General metric sizes are common in Asian manufacturing but may lack the dimensional consistency and tooling availability of standardized sizes.
How do I select the right cross-section for my application?
Cross-section selection depends on groove depth, compression rate requirements, and extrusion risk. Thinner cross-sections (1-2 mm) are suitable for compact assemblies with limited groove depth. Thicker cross-sections (3-5 mm) provide better stability in high-pressure and large-diameter applications. Use our Compression Calculator to validate that your chosen cross-section achieves 15-25% compression in the groove.
Do size charts include groove dimensions?
Yes. Our downloadable size chart PDFs include recommended groove width, groove depth, corner radii, and surface finish for each standard size. These groove recommendations are based on industry best practices and ensure optimal compression rate and gland fill ratio.
Need a Custom Size?
Any ID and cross-section. MOQ starts at 1 piece. Quote within 24 hours.
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