First step when estimating a hole project for insulation is to take all the doors and windows then multiply each one "height times width" to get the SQFT number of each. Add all the doors and windows SQFT together then note that number for later, it will be subtracted out of the total SQFT for the project.
Estimating the SQFT for the ceiling can be done by the SQFT of the floor below. Ceiling insulation thickness can change depending on the city you live in and might need to be considered into the SQFT number for the ceiling insulation. Example if a room 10'x10' that needed 2 feet of insulation in the ceiling It would be multiply 10x10=100 then multiply by 2 to get the needed thickness 100x2=200. [Total= 200 SQFT]
Estimating the total needed stud wall insulation, this isn't like ceiling insulation where different thicknesses can change the needed SQFT number. Most all pre-made and spray-in insulation is already setup so that all they need is a wall size [2x4 2x6] and a SQFT number of the area. To figure the walls just add the total length of all the walls times the height of the walls to get the total SQFT number. [height times width = SQFT] Last subtract the wall SQFT number from the window and doors SQFT number to get the total amount of wall insulation needed for the project.