how do i find out what turns my motor is

[MGR]

don't flame for sounding like a n00b... i need to find out what turns a brushed motor is ( it's de stickered and there's no markings on the can or endbell... i don't want to put it on my XRS and it be over the 15t limit

any help would be much appreciated guys
(it's brushed by the way)

cheers
rich