Short answer
Cannabis potency is the amount of THC in a product. Labels show it as a percentage of weight for flower and concentrates, or as milligrams per serving for edibles. THC is the main psychoactive compound in cannabis. Flower at 20% THC holds 200 mg of THC per gram. A 10 mg edible holds 10 mg of THC. A potency number describes dose. It does not describe quality, taste, or grow method.
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What the numbers measure
Flower labels list THC and THCA. THCA becomes THC when heated. Labs report total THC as THC plus 0.877 times THCA. A sample with 25% THCA and 1% THC comes out near 23% total THC. Distillate vapes and live resin vapes run 60% to 90% THC. Kief and hash sit between flower and distillate. Edibles use milligrams because THC weight is small and serving counts vary.
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Potency rose over time
NIDA tracking of seized US flower shows THC near 4% in 1995 and near 12% in 2014. Legal market flower now sells at 15% to 30%. Concentrates moved higher. A 0.5 g joint of 25% flower holds about 125 mg of THC. That equals 12 standard 10 mg edible servings. Data on long term health effects of high potency products is limited.
how to determine cannabis potency
Testing and label variance
State labs test batches before sale. Rules differ by state. Some states allow a 10% variance between the label and a lab result. Studies of legal products find label error in a share of samples. Treat a potency label as an estimate of dose. Batch IDs and lab reports give more detail.
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Dose matters more than percentage
Two draws from an 80% vape can deliver more THC than a 20% flower joint. Serving size, inhalation depth, and tolerance change the effect. Colorado caps recreational edibles at 10 mg THC per serving and 100 mg per package. Illinois and other states use the same 10 mg unit.
Why potency ties to convenience
Convenience formats push potency up. A vape pen delivers a set high dose in one draw. A pre-rolled joint holds a fixed gram weight. A single-serve edible carries a printed milligram count. Buyers who want a repeatable result pick the format with the clearest number. Potency labels serve that goal. They do not measure terpenes, pesticides, or cure.
How to read a label
- Check total THC, not THC alone.
- Note net weight or serving count.
- Compare milligrams per serving across formats.
- Start low with edibles, 2.5 mg to 5 mg THC.
- Check the batch date and lab report when the store posts one.