How to design an O-ring groove that actually seals
A reliable O-ring seal lives or dies on three numbers: squeeze, gland fill and stretch. This O-ring groove design calculator computes all three from your cross section (CS) and groove geometry and flags anything outside the accepted window, so you can iterate the gland before cutting metal.
Squeeze
Squeeze is the radial compression applied to the cross section: (CS โ groove depth) รท CS ร 100. It is what generates the contact stress that forms the seal. Static seals target roughly 15โ30% squeeze for a robust seal with margin for compression set. Dynamic reciprocating seals run a lower 8โ16% to keep friction, wear and heat under control; rotary seals lower still. Too little squeeze leaks; too much drives compression set, high installation force and premature failure.
Gland fill
Gland fill compares the O-ring cross-sectional area to the groove area โ (ฯ/4 ยท CSยฒ) รท (depth ยท width) ร 100. The sweet spot is 60โ85%. The deliberately empty volume is not waste: it is the room the elastomer needs to expand into when it absorbs heat or fluid. Fill above 90% leaves nowhere for that swell to go, and the ring can over-pressurise the groove and extrude. Fill that is too low lets the ring roll or shift in dynamic service.
Stretch
When an O-ring is installed over a larger groove ID it stretches, which thins the cross section and slightly reduces effective squeeze. Keep installed stretch at or below 5% (8% absolute maximum). The calculator applies a volume-conservation correction so the squeeze and gland-fill figures use the effective CS, not the nominal one.
Use the results as a starting point, then validate against your temperature, pressure and media. Harkesh engineers can review your gland and recommend a compound and tolerance set โ turn any result into a quote in one click.
