In Ca₂RuO₄, the competition of spin-orbit coupling ζ and tetragonal crystal-field splitting Δ_CF has been discussed controversially for many years. The orbital occupation depends on Δ_CF/ζ, which allows us to address this ratio via the optical spectral weights of the lowest intersite Mott-Hubbard excitations. We study the optical conductivity of Ca₂Ru_0.99Ti_0.01O₄ in the range of 0.75–5 eV by ellipsometry, using the large single crystals that can be grown for small Ti concentrations. Based on a local multiplet calculation, our analysis results in 2.4≤Δ_CF/ζ≲4 at 15 K. The dominant crystal field yields a ground state close to xy orbital order but spin-orbit coupling is essential for a quantitative description of the properties. Furthermore, we observe a pronounced decrease of Δ_CF with increasing temperature, as expected based on the reduction of octahedral distortions.