This is the hardest part for many people! If you purchased cannabis flower from a licensed dispensary, that flower should be accompanied by lab testing, which shows the percent of THC or CBD in the flower. Unfortunately, different labeling regulations do not make this information universal. If you grew your own cannabis at home, knowing the potency of THC or CBD will be impossible without lab testing. You can, however, research strain guides that provide a general idea of the total cannabinoids in a specific strain.