Take the measurements of area requiring insulation. This product covers 135.13 sq ft per bag. Take the sq ft required and divide by sq ft per bag to get number of bags required. If you area is 10’ X 20’, you will need 200 sq ft and will need to purchase 2 bags of material.
200/135.13 = 1.48 bags to complete or 2 bags. Hope this helps with your project.