What is the correct amount of topsoil needed for a proper lawn?

It is recommended by experts in the landscape industry that at least four to six inches of topsoil be used when a lawn is being established. The deeper the topsoil layer, the greater the opportunity the turfgrass has to develop a dense and healthy root system. As the thickness of the topsoil increases, greater amounts of moisture are then able to be retained and captured by the turfgrass root system.