Total THC is not measured directly. The lab measures THCA and Δ9-THC separately, usually by HPLC, then combines them, applying 0.877 to the THCA because decarboxylation removes CO2 and about 12.3% of the molecule's mass. It is the figure most labels and legal limits use.
In practice
A COA shows THCA 22.0% and Δ9-THC 0.8% w/w. Total THC = 0.8 + 0.877 × 22.0 = 0.8 + 19.3 = 20.1%. Adding the two lines without the factor (22.8%) inflates the figure by about 2.7 points, a common error or trick. Real-world conversion during smoking or cooking is lower than the theoretical total because of losses.
Total THC (% w/w) = Δ9-THC + 0.877 × THCA. The factor is the molecular weight ratio, 314.5 / 358.5. Some rules define it differently (for example, also counting other THC isomers); check the definition the lab applied.
Don't confuse with
Myth check
House position: most flower people believe tests in the mid-20s to 30s really tests mid-teens to low 20s. See buyer beware.
THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.HPLC (high-performance liquid chromatography) separates compounds dissolved in a liquid under pressure; it is the standard cannabis potency method because it measures acid cannabinoids without heating them.Decarboxylation is the loss of a carboxyl group as CO2 that turns acid cannabinoids such as THCA and CBDA into neutral THC and CBD, quickly with heat, slowly with time.CO2 enrichment raises carbon dioxide in a sealed grow space from about 420 ppm to roughly 800–1,500 ppm, letting plants use higher light intensities productively.A COA (certificate of analysis) is a lab's signed report of what it measured in a specific sample, such as cannabinoids, terpenes, moisture and contaminants, with methods and limits.Total cannabinoids is the sum of all cannabinoids a lab measured in a sample, usually reported in % w/w, with acid forms either summed raw or decarboxylation-adjusted.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Total CBD is a calculated figure, CBD plus 0.877 × CBDA, estimating the maximum CBD a sample could yield after full decarboxylation.
