  Femtoscopy is providing information on system size and its dynamics in
heavy-ion collisions. At ultra-relativistic energies, such as those obtained at
the LHC, significant production of pions, kaons and protons enables femtoscopic
measurements for these particles. In particular the dependence of system size
on pair momentum and particle type is interpreted as evidence for strong
collective flow. Such phenomena are naturally modeled by hydrodynamics. We
present calculations within the 3+1D hydrodynamic model coupled to statistical
hadronization code THERMINATOR 2, corresponding to Pb--Pb collisions at
$\sqrt{s_{\rm NN}}=$2.76 TeV. We obtain femtoscopic radii for pions, kaons, and
protons, as a function of pair transverse momentum and collision centrality. We
find that an approximate universal scaling of radii with pair transverse mass
and final state event multiplicity is observed, and discuss the consequences
for the interpretation of experimental measurements.
