I just hit 15,000 square yards of carpet installed in my career, and the number felt way bigger than I expected.
It hit me when I was doing the math for a quote on a 400-yard job in a new apartment complex, and I realized my knees have felt every single one of those yards.
Ever think maybe the knee pads are the problem? If you need that many, maybe the floor is just too hard or you're working in a way that hurts your body. The real math is figuring out how to not wreck your knees in the first place. Sometimes the gear is a sign you should change the job, not just keep replacing pads.