Groceryman and boombada are both correct.
The drumometer will tell you how many beats you played in a certain amount of time. However, if you don't have a metronome you should get that first. A metronome will help you to play at a consistent tempo.
You can set the metronome to a certain speed - let's say 60bpm
If you play quarter notes you are playing 60 hits per minute (Metronome marking x 1)
If you play eighth notes you are playing 120 hits per minute (mm x 2)
If you play triplets you are playing 180 hits per minute (mm x 3)
If you play sixteenth notes you are playing 240 hits per minute (mm x 4)
Not only will you be able to tell how many hits per minute, but you will be playing in time.