Guide · Hemp · Product Classification

Total THC vs. Delta-9: How the Number Is Calculated and Which Law Uses It

A certificate of analysis can report delta-9 THC, THCA, total THC, and milligrams per serving, and each figure answers a different legal test. This guide explains how total THC is calculated, how a percentage limit differs from a per-container limit, and which measure federal, Illinois, and Missouri law apply in 2026.

By Lincoln Square Law · 8-minute read

The question a lab report cannot answer by itself

A laboratory can measure a product accurately and still leave the legal question open. Delta-9 THC, THCA, total THC, and milligrams per container are different numbers, and in 2026 different laws use different ones. The federal hemp definition has measured delta-9 alone since 2018, and it moves to total THC in two steps, on November 12 and December 11, 2026. Illinois and Missouri each enacted hemp laws that count THCA and impose a per-container limit. Missouri adds tests that use no threshold at all. A product team that reads one figure from the certificate of analysis and calls the product “compliant” can be right under one law and wrong under another on the same day.

How total THC is calculated

THCA, tetrahydrocannabinolic acid, is the form in which THC exists in the raw plant. Heat removes a carboxyl group and converts THCA into delta-9 THC, a reaction called decarboxylation. U.S. Department of Agriculture hemp regulations define total THC as the value determined after decarboxylation, or after applying a conversion factor when the test method does not decarboxylate the sample, reported on a dry weight basis. When liquid chromatography is used, which leaves THCA intact, total THC equals 0.877 times THCA plus THC (7 C.F.R. 990.1). The 0.877 factor accounts for the weight lost when the carboxyl group leaves the molecule.

The method matters. Gas chromatography heats the sample, so THCA is converted during the test and the result already reflects total THC. Liquid chromatography reports THCA and delta-9 separately, and the total has to be calculated (7 C.F.R. 990.1, definition of post-decarboxylation). A certificate that reports only delta-9 from a liquid chromatography run does not show total THC.

Hypothetical. Flower tests at 0.2 percent delta-9 THC and 20 percent THCA by liquid chromatography. Total THC is 0.877 × 20 + 0.2, or 17.74 percent. The flower passes a 0.3 percent delta-9 test and fails a 0.3 percent total-THC test by a wide margin.

Measurement uncertainty is a cultivation rule

USDA’s regulations also define an acceptable hemp THC level by applying the laboratory’s measurement of uncertainty to the reported total delta-9 THC result. A sample is acceptable if the resulting range includes 0.3 percent or less, and USDA’s own example is a 0.35 percent result with an uncertainty of plus or minus 0.06 percent, which qualifies because the range runs down to 0.29 percent. The same definition states that it does not change the statutory definition of hemp (7 C.F.R. 990.1).

That rule was written for USDA’s hemp production program, which governs sampling and testing of growing plants. We have not found a comparable measurement-uncertainty rule for the new per-container limits on finished products. A product near the container limit should not rely on the cultivation rule’s margin.

Percentage limits and container limits measure different things

A dry-weight percentage measures how much of the material is THC. The 0.3 percent limits in the federal, Illinois, and Missouri definitions apply to the plant and, for intermediate products, to combined total THC and similar-effect cannabinoids. A per-container limit measures the absolute amount in the retail package. The new federal limit for final products is greater than 0.4 milligrams combined total per container of total THC, including THCA, and other cannabinoids with similar effects as determined by the Secretary of Health and Human Services (7 U.S.C. 1639o(1)(C)(iv)(III), as amended). Federal law defines the container as the innermost wrapping, packaging, or vessel in direct contact with the final product for retail sale (7 U.S.C. 1639o(3)(C), as amended).

Hypothetical. A gummy contains 2 milligrams of hemp-derived delta-9 THC in a 5-gram piece, which is 0.04 percent by weight. It passes a 0.3 percent test. A jar of 10 gummies holds 20 milligrams, 50 times the 0.4-milligram container limit. A single gummy sold in its own packet still holds 2 milligrams and still exceeds the limit.

Because the container limit counts similar-effect cannabinoids, the calculation is not limited to delta-9 and THCA. Under federal law, the list of those cannabinoids is to come from HHS and FDA, and as of this writing FDA has not published it. Illinois supplies its own list in the Illinois Hemp Act, which the Illinois Department of Revenue says includes delta-8 THC, THC-P, HHC, and THC-O (410 ILCS 707/15).

Which measure each law uses in 2026

Federal law through November 11, 2026. Hemp is measured by delta-9 THC concentration of not more than 0.3 percent on a dry weight basis (7 U.S.C. 1639o(1), prior text). Separately, USDA’s production rules already test growing hemp for total THC (7 C.F.R. 990.1).

Federal law, November 12 through December 10. Only the exclusions for products containing cannabinoids that are not capable of being naturally produced by the plant apply (Pub. L. 119-103, div. B, sec. 2019). For all other products, the total-THC definition and the container limit are not yet in effect, and the prior delta-9 definition continues to describe them.

Federal law from December 11, unless Congress acts. Total THC including THCA at not more than 0.3 percent dry weight, the intermediate-product limit, the 0.4-milligram final-product container limit, and the synthesized-cannabinoid exclusion all apply (7 U.S.C. 1639o, as amended).

Illinois from November 12. The Illinois Hemp Act uses total THC including THCA, the same exclusions, and the 0.4-milligram container limit, with the state’s own similar-effect list (Ill. Dep’t of Agriculture, IB-2026-06).

Missouri from November 12. Missouri’s Intoxicating Cannabinoid Control Act uses total THC including THCA for the hemp definition and a 0.4-milligram container limit for final products (RSMo 195.900.2(3)). Two of its November 12 categories use different tests altogether. Smokable or vapeable raw flower is covered if it contains any amount of THCA. A solid edible is covered if it contains hemp-derived delta-9 THC above the naturally occurring concentration in the source plant (RSMo 195.900.11(1)(a)). Neither test has a numerical threshold to stay under. Our Missouri briefing explains how those categories fit the Act’s two effective-date tracks.

Reading a certificate of analysis for legal use

Before relying on a certificate, confirm that it identifies the sample and the lot actually sold, states the method (gas or liquid chromatography), reports THCA separately or reports a decarboxylated total, and reports results on a dry weight basis where a percentage limit applies. Confirm that it covers the cannabinoids on the relevant similar-effect list, not only delta-9 and THCA. For a final product, confirm the net weight or volume and servings, so the per-container figure can be calculated. A certificate cannot tell you whether a cannabinoid was synthesized outside the plant. That fact comes from the formulation and supply-chain records.

Keep the arithmetic with the certificate. Our hemp product compliance worksheet gives a SKU-by-SKU format. For each SKU, record the reported values, the formula used, the container contents, and the result for each law that applies. Someone who was not involved in product development should be able to reproduce the conclusion.

When to retest and reclassify

Retest or reclassify when the formula, cannabinoid source, extraction or conversion process, serving size, container size, or laboratory changes, and when the governing law changes. In 2026 that includes November 12 and December 11. A product can cross a line without any change to its label, for example when a supplier substitutes an isolate or a packaging change adds servings to the container.

What to ask counsel about your test results

For each SKU, which measure applies in each state where it is sold, and on what date? Do our certificates report THCA and the similar-effect cannabinoids on the Illinois list? Which products depend on a per-serving figure that does not meet a per-container limit? Do any Missouri products contain any THCA in flower form, or hemp-derived delta-9 above natural levels in a solid edible?