Total THC and Total CBD: What They Mean and How They Are Calculated

What "total" means

"Total THC" and "total CBD" are calculated numbers. They combine the neutral compound (THC or CBD) with its acid precursor (THCA or CBDA) so that the report reflects the potential amount of the neutral compound if all of the acid were converted by heat. Totals exist because some testing methods keep the acid forms intact and report them separately. This page explains the arithmetic for understanding labels. It is not dosing information.

The formulas

The US Agriculture Department's hemp rule defines the decarboxylated value as a molecular mass conversion ratio that sums delta-9 THC and 87.7% of THC-acid, written (delta-9 THC) + (0.877 x THCA). [1] The rule states that for liquid chromatography, which keeps THCA intact, Total THC = (0.877 x THCA) + THC. [1]

The University of Georgia Cooperative Extension writes both versions: % Total THC = % THC + (% THCA x 0.877), and % Total CBD = % CBD + (% CBDA x 0.877). [2] Whether any government sets a CBD-specific total formula was not verified for this page.

Why 0.877

The acid form has a carboxyl group that is lost during decarboxylation, so the acid molecule is heavier than the neutral molecule. The factor corrects for the additional weight of that group. [2] The USDA rule describes it as a molecular mass conversion ratio. [1] Without the factor, adding the two rows would overstate the potential total.

Worked arithmetic (invented numbers)

Suppose a made-up report lists THC 0.5% and THCA 10.0% on the same basis. Total THC = 0.5 + (0.877 x 10.0) = 9.27%. The numbers are for illustration only and are not typical of any product.

What a total assumes

• Complete conversion. Real heating may not convert everything. A review of cannabinoid analysis notes that decarboxylation by heat adds variability from reaction kinetics and possible decomposition. [3]
• Same basis. The USDA rule requires total THC to be reported on a dry weight basis. [1] A figure on another basis is not directly comparable.
• A sound method. NIST described interfering compounds that can inflate reported delta-9 THC in some chromatography methods. [4]
• An uncertainty. The USDA rule says a laboratory reporting hemp total THC must also report the measurement of uncertainty. [1]

Direct heated methods

A gas chromatography result does not include the acid forms and represents total cannabinoid content. [2] The USDA rule also says gas chromatography converts THCA to THC in the instrument, so the test calculates total potential THC. [1] In that case the lab should not apply the 0.877 factor again; check the method line on the report. See testing methods.

A legal note

For US hemp compliance, the rule says the acceptable hemp THC level applies the measurement of uncertainty to the reported total delta-9 THC on a dry weight basis; the example given is a reported 0.35% with uncertainty of plus or minus 0.06%, giving a range that includes 0.3%. [1] This describes a US federal hemp-plan rule as read on 2026-10-22; state rules differ, laws change, and this is not legal advice. See cannabis laws by country.

Related guides

Start with how to read a cannabis COA, then THC vs THCA on a label and CBD vs CBDA on a label.