"Doing Numbers" refers to when something sells alot of units or a respectable amount of units. Mostly used on forums to predict, celebrate or ridicule the performance of an album that just hit the market. In hiphop forums, arguments over successful/superior albums can sometimes result in comparing Soundscan/Hits Daily Double sales.

For an album to "do numbers", usually it needs to sell AT LEAST 100k in the first week, go #1 on the chards, and go GOLD or PLATINUM at some point.. otherwise it is a dud