Total CBD is calculated the same way as total THC. The lab measures CBDA and CBD separately and combines them, multiplying CBDA by 0.877 to account for the CO2 lost on decarboxylation. THCA and CBDA are isomers, so the conversion factor is identical.
In practice
A hemp-type COA reports CBDA 11.5% and CBD 0.4% w/w. Total CBD = 0.4 + 0.877 × 11.5 = 0.4 + 10.1 = 10.5%. Breeders use total CBD alongside total THC to place a plant in its chemotype class: the same plant's total THC might read 0.4%, giving a CBD:THC ratio of about 26:1, a type III plant.
For anyone working under a hemp THC limit, the important number is usually total THC, not total CBD. A high-CBD plant still makes some THCA, because CBDA synthase isn't perfectly specific.
Total CBD (% w/w) = CBD + 0.877 × CBDA. Factor = 314.5 / 358.5 (molecular weights of CBD and CBDA).
Don't confuse with
- CBDA: one input to the calculation, not the total.
- Total cannabinoids: the sum of all measured cannabinoids.
- CBD content on a product label: may be per serving or per container, not % w/w.
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.CBDA (cannabidiolic acid) is the acid cannabinoid made by CBDA synthase from CBGA; it dominates hemp-type and CBD-type cannabis and decarboxylates to CBD.CBD (cannabidiol) is a non-intoxicating neutral cannabinoid formed when CBDA decarboxylates; hemp-type and CBD-dominant cannabis make it mainly as CBDA in their trichomes.Total THC is a calculated figure, Δ9-THC plus 0.877 × THCA, estimating the maximum THC a sample could yield after full decarboxylation.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.The chemotype ratio is the balance of a plant's main cannabinoids, usually THC to CBD, classing plants as type I (THC-dominant), II (mixed), III (CBD-dominant), IV (CBG) or V (near-zero).CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant.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.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.
