Calculating “Total THC” or “Max THC”

Use whatever information you have available to calculate and convert potency values using the calculator below!

​Simply input a value into the available cell(s) and then press “Enter” to calculate the associated result in the shaded cell.

NOTE: To convert from mg/mL to mg/g, density must be determined. Density can be determined by accurately weighing one mL of the product and recording the result in g/mL.

NOTE: Total weight and Total THC to mg/g conversions are only accurate if the product is homogeneous.

​Interested in calculating Total THC or Total CBD? Scroll down and read below!

What is Total or Max THC?

“Total” or “Max” THC refers to the theoretical maximum decarboxylated THC that is present in a product. This value is calculated using a simple formula:

THC + (THCa x 0.877) = Total/Max THC

The Cannabis plant does not actually synthesize decarboxylated cannabinoids. Instead, most of the THC and other cannabinoids are present as cannabinoid acids like THCa, CBDa, or CBGa. The cannabinoid acids, including THCa, are non-psychoactive. They will not cross the blood brain barrier to interact with cannabinoid receptors in the brain. That being said, there is research currently exploring some of the unique therapeutic effects that cannabinoid acids may elicit.

The distinction between THC, THCa, and Total THC is important so that consumers understand the potential effects of the products they choose to consume. Total THC or Total CBD calculations are particularly important for products intended to be smoked or vaporized. For infused edibles and other cannabinoid products, Total THC or Total CBD can actually be misleading.

But where did that 0.877 number come from?

The 0.877 value in the formula represents the percent of THC that remains once THCa has been perfectly decarboxylated. This can be manually calculated by dividing the molecular weights of THC and THCa. What this number means is that the weight of THC is only 87.7% that of THCa.

THC’s molecular weight is 314.45 g/mol. THCa’s molecular weight is 358.4773 g/mol, substantially heavier than THC. When you divide 314.45 by 358.4733, you are left with 0.8771922 which is then rounded down to 0.877.

Molecular Weight of THC / Molecular Weight of THCa = Decarboxylation Correction Factor

his process of calculating total THC has now been published in several peer-reviewed scientific research articles.

Why does THC weigh less than THCa? Aren’t they basically the same?

THCa and THC are different structurally due to the addition of a carboxylic acid functional group in the THCa molecule. A carboxylic acid functional group is essentially a carbon dioxide molecule. When THCa is warmed, the carboxylic acid group pops off the molecule and is expelled as CO2. This loss of carbon dioxide reduces the weight of the molecule. This is why it is not correct to simply add THCa and THC to calculate total THC. Simply adding these values without applying the 0.877 correction results in inflated potency values that are misleading to consumers and do not accurately represent the potential of the product.


Note the carboxylic acid functional group on the right side of the molecule! ​THCa weighs more than THC because it is a bigger molecule!

Note: Carbons and Hydrogens are not labeled in this diagram because they are implied.


In THC, the carboxylic acid functional group has been removed due to exposure to heat or with age!

Does this formula work for all cannabinoids and cannabinoid acids?

This calculation using the 0.877 decarboxylation correction factor should only be used to calculate Total THC or Total CBD. If calculating total decarboxylated cannabinoid content of other cannabinoids, it is important to actually look up the molecular weights and divide them to see if the decarboxylation correction factor is the same. The correction factor may be slightly different between other cannabinoids.