I was just wondering if anyone has a good idea on how to calibrate or calculate how much area I can cover with a backpack sprayer. I've used it many for spot treatments but I want to start using it for larger areas. I've looked for info about how much area it can treat online but I've found nothing. I've tried to calculate myself and I've come up with 4 gals can treat 4100 sq ft. Does that even sound right? The Sparyer is a Solo #475 Backpack Sprayer D475. If anyone could help me on this matter that would be nice.