How do you check fps on paint ball marker?

Answer 1

you use a Chronograph (Chrono for short) they measure the FPS as a paintball flies away, a field will always have them and you can buy one for home use if you want

Answer 2

You shoot it over a chronograph. All paintball fields have them.

Answer 3

Shooting it over a chronograph is the only way to be sure. You can guess depending on what it says in the manual, like if it says +5 fps per quarter turn.