Worksheets for the Surface Area of a Cone and for the Volume of a cone. The surface area of a cone is: πrs + πr2 Think about this formula as (3.14 x radius x slant) + (3.14 x radius x radius) 3.14 is pi. The radius is the measure from the middle of the cone to the side and the slant is the measure from the point of the cone to the open circle of the cone. The volume of a cone formula is 1/3πr2h which means you will calculate 3.14 x radius x radius x height ? 3 (3.14 is pi) Notice that the slant (s) is not needed in the volume formula.