I have no idea but I do know they are usually all different. I keep track of my weights in a log so I just assume that it weighs the standard 45lbs. Ie. If I'm doing upright rows with a 45 on each side I write down 135lbs x Reps. Since I'm the only one who sees the log who cares if it's not 100% correct. I just use it to gauge strength increases.