When referring to a drum set, manufacturers list sizes differently. Some list the diameter first and the depth second. Others do the opposite. The best thing to remember is that the diameter is usually always going to be the larger number, unless it is a custom make. Regardless of whether the specifications say it is a 9x10 or 10x9, the diameter is 10” and the depth is 9”. However, this isn't necessarily the case when you start looking into world percussion. Things like Conga's, Djembe's, or Tumba's are usually the opposite. The depth of the drum ends up being the larger number. If you need to find replacement heads and can not remember what size drum you purchased, the best way to measure the drum is to take the rims off and then measure the shell directly across. When looking for heads, the depth will not matter unless you are looking for a certain sound. However, that is a whole other concept to replacement drum heads.