A new fully experimental method to determine the backscattering coefficient and the ballistic ratio of n- and p-FDSOI and multigate nanodevices is proposed in this paper. This technique is the first one that takes multisubband population, carrier degeneracy, and short channel effects into account. Owing to self-consistent Poisson-Schrodinger simulations, common assumptions such as one subband occupied by carriers are investigated. For the first time, universal abaci, which are functional whatever the architecture dimensions and the gate/substrate polarizations, have been developed in order to accurately extract backscattering coefficients for n- and p-FDSOI MOSFETs, both in linear and saturated regimes.