We’ve received many customer calls and visitor questions over the years concerning one seemingly arbitrary number. This number is featured in the important calculation for “THCmax”, or total available THC as we like to call it. The calculation looks something like this:
THCmax = THC + 0.877 * THCA
This number is not at all arbitrary, but where does it come from? In a simple phrase: the structure of cannabinoid molecules.
As you may know, the plant-made versions of the major cannabinoids, sometimes called cannabinoid acids, need to be “decarbed”, or decarboxylated, before they can assume their full active effects. This decarboxylation is why it’s called a decomposition reaction — one molecule becomes two. In our case, one of these molecules is always CO2, (carbon dioxide being the source for decarboxylate). The other molecule is the “active” or “neutral” cannabinoid itself.
The number 0.877 is actually fixed in nature, and it’s based on the ratio of the masses of the cannabinoid molecules. Most major cannabinoids (THC, CBD, CBG, CBC, but not CBN) have the same molecular formula: C21H30O2, for 21 carbons, 30 hydrogens, and 2 oxygens. The equivalent cannabinoid acids (THCA, CBDA, CBGA, and CBCA, respectively) are “neutral” cannabinoids that are “wearing” a CO2 molecule, changing their molecular formula to C22H30O4 with the addition of one carbon and two oxygens.
Each element in a molecule has a measurable weight, and the most common weight of an element is usually the largest number in an element’s box on the periodic table. Carbon has an atomic mass of approximately 12.011, hydrogen about 1.008, and oxygen almost exactly 16.
We can calculate how much each molecule of THC weighs, like this:
THC’s molecular weight = 21 Carbons (12.011) + 30 Hydrogens (1.008) + 2 Oxygens (16.000)
THC’s molecular weight = 314.47
We can calculate the same for THCA:
THCA’s molecular weight = 22 Carbons (12.011) + 30 Hydrogens (1.008) + 4 Oxygens (16.000)
THCA’s molecular weight = 358.48
The molecule released during “decarb”, CO2, has a molecular weight of about 44.01. If we add THC’s 314.47 and CO2’s 44.01, we get the molecular mass of THCA, 358.48. The universe is making sense! So far so good. If we take this a step further, we realize that THCA is, in fact, not entirely THC. It’s only 314.47 / 358.48 = 0.8772 or 87.72%. There’s our 0.877! The remaining 12.28% is CO2, which bubbles away as a gas during decarboxylation – the bubbling of a full melt hash or a dab on a hot nail illustrates this process.
Now, the goal of the available THC calculation is to find, under absolutely ideal conditions, the maximum amount of “active” THC that can be derived from a sample. If THCA is only 87.72% THC, it only makes sense that we account for that fact in our available THC calculation; Multiply the amount of THCA by 0.877 before adding it to the amount of already “activated” THC. Put another way, a gram of 100% pure THCA contains 0.877 grams of THC and 0.123 grams of CO2.
The same exact “activation multiplier” can be used to calculate available CBD, CBG, or any other cannabinoid with a molecular formula of C21H30O2. Some may have noticed that the American Herbal Pharmacopeia blurb about available cannabinoid content features a multiplier of 0.878 for CBGA; this is because CBGA’s molecular structure contains two more hydrogen atoms, for a formula of C22H32O4. When CBGA decarboxylates into CBG, the two hydrogen atoms are retained, and CBG thus has two more hydrogen atoms in its structure than THC or CBD. The same math from above with the molecular weights of CBGA and CBG (360.75 and 316.74 respectively) yield a conversion factor of 0.8780, slightly different than the 0.877 for THCA to THC.
For the -varin class of cannabinoids, THCV being the most well-known (but also including CBDV, CBGV, CBCV, and their respective acids CBDVA, CBGVA… etc.), we need a different activation number because the molecular masses aren’t the same: cannabivarins are missing two carbons and four hydrogens compared to their regular cannabinoid cousins, giving us a molecular formula of C19H26O2 (mass of 286.42), and C20H26O4 (mass of 330.43) for their acids. Our “activation multiplier” for the -varin class is 0.8668 instead of 0.8772. Close, but not the same!
We hope this answers some of your questions about our favorite herbal product, or perhaps piques your interest to learn more about chemistry. If you have any more questions about the chemistry of Cannabis, our knowledgeable staff are more than pleased to answer them!
Check out our other blog posts for more curious topics of discussion, and refer to this page for an explanation of all the cannabinoid values we report on our certificates of analysis.
TL;DR: The seemingly arbitrary number 0.877 is a ratio of molecular masses, specifically that of THC divided by that of THCA. If you multiply the amount of THCA by 0.877 and add the amount of already “active” THC, you find the maximum amount of THC remaining after complete decarboxylation. THCA is about 87.7% THC and 12.3% CO2 by mass.