In almost every pic you see of Arnold flexing, his arms look 20-21 inches right? It's safe to assume he's pumped up in the photos. So it's not farfetched to think his arms were 19.5 inches cold. My arms are 15.5 inches cold and I can pump them up a good inch after I work them out. If his arms were 21 inches cold, then he should be able to pump them up to 23 or 24 inches. Ronnie Coleman's arms measure that large, yet Arnold comes nowhere close to that. You also have to realize that Arnold had relatively weak triceps, forearms, and shoulders which created the illusion his biceps were much larger than they were.