Each machine has a rated 'capacity', which is the maximum number of images the manufacturer recommends that it make per month. So, even if a copier is rated at 50,000 images per month, it probably makes closer to 10,000. Along with capacity, it is useful to know the rated imaging speed. Machines don't necessarily run at the rated speed, either ever, or under ordinary use, but speed is a good way to categorize machines. It can be unclear just what to include in your estimates of paper use costs.
Some costs are easy, such as the cost of purchasing paper.
This can get quickly out of hand. The point of analyzing paper use is to see costs that you might save. Thus, you can assume that you will have a printer regardless, but you might use it less, and so it might last longer. Last year the copiers were used at the following rates. Speed is in copies per minute.