How do I know how much soil to order to build up from erosion in my yard

How do I know how much soil to order to build up from erosion in my yard. My house is located on the down slope of a hill, there is a lot of erosion and I feel that it's time to add some fill at least to my front yard. I am in Maryland, and my soil has a heavy concentration of clay in it. I am planning on aerating the soil that is there and planting seed for grass. But I just don't know what type of soil to add. I read that you suggested a mix of sand topsoil and sawdust?