lf the crystal filed splitting energy for octahedral complexes is ${\Delta }_0$ and for tetrahedral complexes is $\Delta t$, the two are related as

The crystal field splitting energy in case of tetrahedral complexes where only four ligands approach the central metal ion causing weak field around it is smaller than the crystal field splitting energy of octahedral complexes where six ligands approach the central metal ion and create a strong field around it. The two are related as ${\mathrm{\Delta }}_t=\frac{4}{9}{\mathrm{\Delta }}_{\mathrm{o}}$