ISO 3601 O-Ring Standard — Dimensions, Groove Design & Compression Calculator

ISO 3601 is the international standard that defines the dimensions, tolerances and groove (gland) design for elastomeric O-rings in fluid power and general engineering applications. Part 1 tabulates the preferred inside diameter and cross-section size series; Part 2 specifies groove depth, width and corner radius for four application types — static face, static bore, dynamic reciprocating and dynamic rotary — so that the installed O-ring achieves the recommended compression squeeze and gland fill for reliable sealing.

Established gland-design practice targets 15–30% radial compression for static (face and bore) seals, 10–20% for dynamic reciprocating seals (pistons and rods), and 5–15% for dynamic rotary seals. These percentage bands are seal-handbook design practice rather than clauses of ISO 3601 — ISO 3601-2 specifies the groove DIMENSIONS (depth, width, corner radius) from which a squeeze follows, not the target percentages themselves. Higher squeeze increases sealing contact stress but also increases friction, heat generation and wear, so dynamic seals use a lower range. The MechanixCalc calculator reports GOOD, LOW or HIGH against these practice bands and badges them as engineering estimates.

ISO 3601 is the international metric O-ring standard, defining a preferred inch-derived series and a pure metric size series used across Europe, Asia and most of industry. SAE AS 568 is the North American aerospace size standard, defining a predominantly inch-based series with tighter aerospace tolerances. The two cover overlapping but not identical ring sizes. The MechanixCalc calculator ships the AS568 series only — 202 sizes across the 000, 100, 200 and 300 series — so if you need the ISO 3601-1 metric cross-sections (1.80 / 2.65 / 3.55 / 5.30 / 7.00 mm), size them from the ISO tables rather than from this tool.

ISO 3601-4 covers anti-extrusion (back-up) rings, which are required when system pressure pushes the elastomer into the diametral clearance gap. The pressure threshold depends on the elastomer hardness (Shore A), the gap size and the elastomer type — typically around 5–10 MPa for NBR without a back-up ring. A single PTFE back-up ring on the low-pressure side extends the limit to roughly three times that value; double back-up rings handle up to about six times. Beyond this, a different seal technology should be considered.

You can use it during a free 30-minute preview with no sign-up required. A free 14-day account trial unlocks every MechanixCalc calculator with no credit card needed. The branded PDF engineering report and saved calculations are included in the free 14-day trial and in every paid plan.