Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory.
In sp3 hybridisation,
1s-oribital and 3p orbitals are mixed to form 4 equivalent sp3 orbitals.
So every sp3 orbital contains 1/4th of s-orbital and 3/4th of p-orbitals.