Billboard magazine has published their top 40 money making musician for 2013. Their list ranks the musicians by their earning from the last 12 months. Billboard complied this list with data supplied by Nielsen SoundScan, Nielsen BDS, YouTube and Billboard Boxscore. The earnings were calculated by including income such as "touring, recorded-music sales, publishing royalties and revenue from an array of digital music and video services for downloads, as well as on-demand and noninteractive streaming."
See the complete list here: