How to read THCa percentages

A certificate of analysis showing 28% THCa does not mean 28% of the flower is active THC. It means 28% of the dry weight is THCa in its raw, acidic form. When that converts to delta-9 THC through decarboxylation, the resulting amount of active THC is lower because the molecule loses mass when the carboxyl group is removed.

The conversion formula

The standard formula used across the industry is:

Total potential THC = (THCa x 0.877) + delta-9 THC

So a flower at 28% THCa with 0.2% delta-9 THC has a potential THC concentration of roughly 24.7% after full decarboxylation. In practice, conversion efficiency through smoking or vaporizing is not 100%, so the actual delivered dose is lower than the calculated maximum.

What different percentages mean in practice

20 to 24% THCa (most greenhouse strains): moderate potency, a reasonable starting point for users with some experience
25 to 29% THCa (indoor strains): higher potency, more pronounced effects from a smaller amount of flower
30% and above (exotic strains): very high potency, fast onset, and a narrow margin for error for less experienced users

Why percentage is not the whole picture

Two strains at the same THCa percentage can produce very different experiences. The terpene profile, the presence of minor cannabinoids like CBD, CBG, and CBN, and the quality of the cultivation and cure all shape the final effect. A well-grown 22% greenhouse strain with a rich terpene profile can be more satisfying than a 30% exotic that was harvested early or dried poorly. Read the COA for the full cannabinoid and terpene breakdown, not just the headline THCa number.

Dosing guidance

If you are new to THCa flower or returning after a break, start small regardless of the percentage on the label. One or two draws from a pipe or vaporizer is enough to gauge your response. Wait at least 15 minutes before taking more. With higher-potency strains, significantly less material is needed to reach the same effect as lower-potency flower.