In case of gravity–capillary waves, where surface tension affects the waves, the dispersion relation becomes:
with σ the surface tension (in N/m).
For a water–air interface (with  and ) the waves can be approximated as pure capillary waves – dominated by surface-tension effects – for wavelengths less than . For wavelengths above  the waves are to good approximation pure surface gravity waves with very little surface-tension effects.