I actually used two methods to be certain.
Before assembly I had weigh every piece of tube and plate on a small industrial electronic scale before welding together. Weigh the Mig wire roll before and after welding and added the lot together plus paint and got total weight.
To check I added the total meters of square and round tubing used together and calculate the linear meters of each section with weight per meter. Added the weight of plates/brackets/paint and welding wire used together and the result well within a quarter kilo of the first method.
