O-Ring Gas Permeation and Leak Rate Calculator
Estimate steady gas permeation through an intact squeezed O-ring from material permeability, pressure differential, contact length and seal condition.
Enter the operating condition and calculate.
How to use
- Confirm the task is steady permeation screening through an intact O-ring; this model does not predict defects or installation leakage.
- Select Helium for the ±50% screening band, or Other gas for a nominal estimate only.
- Enter permeability F for the exact gas, elastomer compound and temperature, including any 10−8 table multiplier.
- Enter contact length D in inches, positive pressure differential ΔP in psi, and a validated condition factor Q.
- Enter squeeze S as a percentage below 100. Choose Calculate; Reset restores the worked example.
- Read the standard cm³/s result first, then converted throughput and annual volume. Correct any red warning before using a result.
- Do not use this estimate when permeability at temperature is unknown, transient diffusion or other leak paths dominate, or qualification and safety decisions require measured evidence.
Equations used
Helium: Lmin = 0.5L; Lmax = 1.5L
L₆₀ = 60L
Tmbar = 1.01325L
TSI = 101325 × 10⁻⁶L
Vyear = 365.25 × 24 × 3600 × 10⁻⁶L
L, Lmin, and Lmax are standard cm³/s; L₆₀ is standard cm³/min; Tmbar is throughput in mbar·L/s; TSI is throughput in Pa·m³/s; and Vyear is annual standard volume in standard m³/year. The conversions use 60 s/min, standard pressure p₀ = 101325 Pa = 1013.25 mbar, 1 cm³ = 10⁻⁶ m³ = 10⁻³ L, and a 365.25-day year. F is actual permeability in standard cm³·cm/(cm²·s·bar); D is effective contact length in inches; ΔP is upstream-minus-downstream psi; Q is the dimensionless squeeze and dry/lubricated condition factor; and S is entered as a percentage and converted to a fraction. The empirical factor 0.7 resolves the correlation’s mixed units.
Assumptions and limits. The squeezed cross-section is approximated as rectangular or square while preserving free area, permeability is proportional to pressure differential, and the entered coefficient represents the exact gas, compound and temperature. Results are order-of-magnitude screening values. Permeation excludes diffusion lag, defects, damage, joints, installation leakage, compression set and aging. Do not use for hazardous-gas containment, personnel protection, safety qualification, or unsupported dynamic applications without applicable testing and standards.