0.877: the difference between THCa and THC

The cannabinoids produced by cannabis initially exist in their acidic form. When heat or light is applied to the plant, the cannabinoids lose a CO2 molecule and transform into their neutral form, a process called decarboxylation.

Breakdown of THCa into THC and then into CBN

Thus, when a cannabis sample is smoked or vaporized, a large portion of the cannabinoids will be decarboxylated by the heat and converted to their neutral form. However, if the same sample is ingested, as long as no heat is applied, the cannabinoid acids will retain their original state.

Analysis and Equivalence of THCa and THC

In HPLC (high-performance liquid chromatography) analyses of cannabis or its derivatives, two lines are combined to determine the maximum total amount of cannabinoid which could be obtained if the sample were completely and thoroughly decarboxylated: in the case of the THC, the percentage of Δ9-THC and the percentage of THCa.

However, if you simply add Δ9-THC and THCa together, you’ll get a number higher than the total THC percentage. Why? Simply because a multiplier of 0.887 is applied when converting THCa to THC.

When THCa loses its CO2 molecule, it transforms into THC, which is a smaller molecule and therefore lighter than THCa. THCa weighs 358 grams per mole, while THC weighs 314 grams per mole. Given this loss, we will have 358/314 = 0.877 molecules of THC per molecule of THCa.

Therefore, the correct formula for calculating the total THC percentage is: % of total THC = % of Δ9-THC + (% of THCa × 0.877).

The same principle is applied when calculating the percentage of CBD total and CBG in total, with a coefficient of 0.877 for CBD and 0.878 for CBG.

However, this coefficient applies only to HPLC analyses and natural decarboxylation. Some Methods for Analyzing Cannabinoids They subject the samples to heat—for example, through gas chromatography—and thereby determine a single total amount of cannabinoid.