O-ring Seal Calculator
Design and verify O-ring seals (ISO 3601 / AS568).
StaticDynamic
O-ring Specification
Housing Dimensions (Nominal & Tolerance, mm)
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Operating Environment & Material
Results

Enter parameters to calculate results.

More Information
Understanding O-Ring Selection and Application

What is an O-Ring?

An O-ring is a mechanical gasket in the shape of a torus (like a doughnut). It is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.

Key Parameters & Calculations

O-Ring Squeeze

The percentage reduction in the O-ring's cross-section diameter when installed. Crucial for sealing; typically 15-30% for static, 10-20% for dynamic.

Squeeze % = [(CS − Gland Depth) ÷ CS] × 100

CS = O-Ring Cross Section Diameter

Gland Fill

The percentage of the groove volume occupied by the O-ring. Should be < 100% (often ~85%) to allow for thermal expansion and swell.

Fill % = (O-Ring Area ÷ Gland Area) × 100

Areas calculated from cross-sections.

O-Ring Stretch (Piston/Shaft)

The percentage increase in the O-ring's inside diameter when stretched onto a groove. Typically kept below 5% to avoid excessive stress and CS reduction.

Stretch % = [(Groove ID − O-Ring ID) ÷ O-Ring ID] × 100

ID = Inside Diameter.

Selection Considerations

  • Application Type: Static (no movement) or dynamic (reciprocating, rotating, oscillating). Dynamic usually needs less squeeze.
  • Material Compatibility: Must suit fluids, chemicals, and temperatures (e.g., NBR, FKM, EPDM, Silicone, PTFE).
  • Pressure: High pressure may need harder materials (durometer), backup rings to prevent extrusion.
  • Temperature Range: Material must operate effectively across the application's temperature extremes.
  • Tolerances & Stack-up: Consider manufacturing tolerances of both O-ring and gland. Calculations should account for worst-case scenarios (e.g., minimum squeeze, maximum fill/stretch) by combining tolerances (stack-up analysis).
  • Surface Finish: Groove and mating part finishes impact sealing and wear, especially dynamically. Smoother finishes are generally better.
  • Eccentricity & Clearance: Misalignment (eccentricity) between mating parts reduces squeeze on one side and increases it on the other. Combined with clearance, this can lead to leakage or extrusion, especially in dynamic seals or under high pressure. Minimize eccentricity and radial clearance.

Disclaimer

This calculator provides recommendations based on standard practices. Always consult manufacturer specifications and perform testing for critical applications. Factors like specific material properties, dynamic conditions, and extreme environments can significantly impact performance.