Brillouin light scattering (BLS) experiments assisted by micromagnetic simulations show that the difference in frequency between counterpropagating spin waves in extended films and multilayers, induced by interfacial Dzyaloshinskii–Moriya interaction (i-DMI), is strongly reduced when lateral confinement is introduced. This poses a limit to the exploitation of BLS to quantify the i-DMI strength in the case of magnetic elements, such as dots and wires, with lateral dimensions below about 400 nm.