ISO 3601 O-Ring Standard — Dimensions, Groove Design & Compression Calculator
ISO 3601 — Fluid power systems — O-rings
ISO 3601 is the international standard for elastomeric O-rings used in fluid power systems and general engineering applications. It is a multi-part standard: Part 1 defines the preferred range of O-ring dimensions (inside diameter and cross-section diameter) and their tolerances; Part 2 specifies the corresponding gland (groove) dimensions — groove depth, width and corner radius — for static face, static bore, dynamic reciprocating and dynamic rotary service. Together, Parts 1 and 2 give designers the complete dimensional framework for selecting an O-ring and designing the hardware groove to deliver the required compression squeeze and gland fill.
Because ISO 3601 governs the geometry of the seal installation rather than the structural integrity of the pressure vessel itself, it pairs naturally with system pressure ratings and elastomer material standards when designing complete sealing systems for hydraulic, pneumatic and process-fluid applications. The MechanixCalc O-Ring & Seals calculator implements the ISO 3601-1/-2 sizing framework directly: it selects the nearest standard O-ring from the preferred series, computes compression squeeze, gland fill and diametral stretch, checks the extrusion threshold and recommends back-up rings — all in a single auditable pass with a PDF engineering report citing the governing equations.
Calculators that implement ISO 3601
What ISO 3601 covers
- Preferred O-ring inside diameter (ID) and cross-section diameter (CS) series with manufacturing tolerances per ISO 3601-1
- Groove depth (H), groove width (W) and corner radius for static face, static bore, dynamic reciprocating and dynamic rotary seals per ISO 3601-2
- Compression squeeze targets by application type: 15–30% for static seals, 10–20% for dynamic reciprocating seals, 5–15% for dynamic rotary seals
- Gland fill percentage — ratio of O-ring cross-sectional area to groove cross-sectional area — target 60–85% to allow thermal expansion while maintaining sealing contact
- Diametral stretch limits (typically 1–5%) to ensure the O-ring seats in the groove without excessive tensile stress that degrades sealing load
- Extrusion pressure limits by elastomer type and diametral clearance gap; guidance on when single or double PTFE back-up rings are required
Parts of the standard
- ISO 3601-1Inside diameters, cross-sections, tolerances and designation codes
- ISO 3601-2Housing dimensions for general applications
- ISO 3601-3Quality acceptance criteria
- ISO 3601-4Anti-extrusion rings (back-up rings)
- ISO 3601-5Inspection dimensions
Governing formulas
Squeeze (%) = (CS − H) / CS × 100where CS = O-ring nominal cross-section (wire) diameter (mm); H = groove depth (mm) per ISO 3601-2 Table 1. Target: 15–30% for static seals, 10–20% for dynamic reciprocating seals, 5–15% for dynamic rotary seals. Values outside the range risk insufficient sealing contact (too low) or excessive friction and extrusion (too high).
Fill (%) = (π/4 · CS²) / (W · H) × 100where CS = O-ring wire diameter (mm); W = groove width (mm); H = groove depth (mm). The numerator is the circular cross-sectional area of the O-ring; the denominator is the rectangular groove area. Target: 60–85%. Below 60% risks loss of sealing contact; above 85% risks over-fill and O-ring damage under thermal expansion.
Frequently asked questions
What is ISO 3601 used for?
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.
What compression squeeze does ISO 3601 recommend?
ISO 3601-2 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. 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 for your specific application type.
How does ISO 3601 differ from SAE AS 568?
ISO 3601 is the international metric O-ring standard, defining a preferred inch-metric hybrid 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 different (predominantly inch-based) size series with tighter aerospace tolerances. The two standards cover overlapping but not identical ring sizes; the MechanixCalc calculator supports both series and lets you filter by standard.
When does ISO 3601-4 require a back-up ring?
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.
Is the ISO 3601 O-ring calculator free?
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 part of a paid plan.
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