O-Ring Groove Calculator (Squeeze, Gland Fill and Stretch)

How it works

Stretch = (seat diameter − O-ring ID) ÷ O-ring ID · stretched cross-section W′ ≈ W × √((ID + W) ÷ (seat + W)) (constant volume) · squeeze = (W′ − gland depth) ÷ W′ · gland fill = (π·W′² ÷ 4) ÷ (gland depth × groove width)

An O-ring seals by being squeezed between the groove bottom and the mating surface. Too little squeeze leaks, too much causes compression set, high friction and assembly damage; seal makers such as Parker recommend roughly 15–30% for static seals and 10–20% for dynamic ones. The groove must also leave room: gland fill above about 85% risks the ring overfilling when it swells or heats up. Stretching the ring onto a piston thins its cross-section, which reduces squeeze — keep stretch under about 5% (2–3% is ideal for pistons).

Worked example

A 3.53 mm cross-section O-ring with a 20.29 mm ID fitted onto a 20.7 mm groove bottom is stretched 2.02%, thinning the section to 3.500 mm. In a 2.8 mm deep, 4.7 mm wide gland it is squeezed (3.500 − 2.8) ÷ 3.500 = 20.0% and fills 73.1% of the groove — both within static-seal ranges.

Sources: Parker O-Ring Handbook ORD 5700 · Wikipedia — O-ring (design)

Frequently asked questions