Total THC vs. delta-9: how the law and the states count THC
Federal law tested crops on total THC for five years while judging products on delta-9 alone. How that split came about, which states closed it first, and what Dec. 11 changes.
The short answer. A delta-9 test counts only the delta-9 THC already in a sample. A total-THC test also counts THCA, which heat turns into delta-9. Federal law judged hemp products by delta-9 alone from 2018, while the USDA tested growing crops on total THC from 2019. On Dec. 11, 2026, as of Oct. 3, total THC becomes the federal measure for all hemp, and many states adopted it first.
The arithmetic, delta-9 plus 0.877 times THCA, is worked through in our THCA vs. THC explainer and on a real report in our COA guide. This page covers the law.
How the two tests got into federal law
| Date | Event | What it measured |
|---|---|---|
| Feb. 7, 2014 | Agricultural Act of 2014, sec. 7606, defines “industrial hemp” for state pilot programs | Delta-9, 0.3% dry weight |
| Dec. 20, 2018 | Agriculture Improvement Act of 2018 adds 7 U.S.C. 1639o | Delta-9, 0.3% dry weight |
| Oct. 31, 2019 | USDA interim final rule for hemp production | Total THC, pre-harvest |
| Jan. 19, 2021 | USDA final rule, effective March 22, 2021 (7 CFR part 990) | Total THC, pre-harvest |
| Nov. 12, 2025 | P.L. 119-37, sec. 781, signed | Total THC, all hemp, from a later date |
| Sept. 2, 2026 | H.R. 6500 signed; THCA flower’s date moves | — |
| Dec. 11, 2026 | Sec. 781 reaches THCA flower | Total THC “(including tetrahydrocannabinolic acid)” |
The 2018 statute said hemp is cannabis with “a delta-9 tetrahydrocannabinol concentration of not more than 0.3 percent on a dry weight basis.” It said nothing about THCA. The USDA, writing the rules for growers, read “concentration” to mean what a crop could deliver once heated.
What the USDA rule requires of growers
The production rule at 7 CFR 990 is still the most detailed federal statement of how total THC is measured. Among its terms:
- Who samples. “Samples must be collected by a sampling agent. Producers may not collect samples from their own growing facilities.”
- When. “Within 30 days prior to the anticipated harvest.”
- What. Cuttings from the flowering tops, “approximately five to eight inches in length.”
- The method. The test must “consider the potential conversion of THCA in hemp into THC,” by “gas or liquid chromatography with detection,” reported on a dry-weight basis with the lab’s measurement of uncertainty. The rule defines the liquid-chromatography conversion as “Total THC = (0.877 x THCA) + THC.”
- The pass mark. A crop passes if the result, after uncertainty is applied, produces a range that “includes 0.3 percent or less.”
- The negligence line. A grower who makes reasonable efforts does not commit a negligent violation unless the crop exceeds “1.0 percent on a dry weight basis.”
- Failing crops. Plants over the limit “constitute marijuana.” They may be remediated by “removing and destroying flower material” or shredding the whole plant and retesting, or destroyed on site or through a DEA-registered reverse distributor.
Every quotation is from 7 CFR 990.1, 990.3, 990.6 and 990.27.
The DEA-registered lab requirement
Section 990.3 says that “after December 31, 2022, States and Indian Tribes shall require that only laboratories registered with the DEA may conduct testing.” The USDA has repeatedly put off enforcing it; its first enforcement-discretion notice dates from Feb. 27, 2020. Its laboratory page says, as of Oct. 3, 2026, that the agency “is delaying until December 31, 2026, the enforcement” of the requirement, citing a notice dated Dec. 23, 2025. The requirement sits in the crop-testing section of the rule; it is not, on its own terms, a rule for the potency reports printed for finished products.
The gap the rule left
The USDA rule regulates a sample taken from a field before harvest. The statutory definition that governs flower after harvest, in a jar or a bag, said delta-9. A finished product could therefore be sold on a report showing low delta-9 and high THCA. That gap, between the crop test and the product definition, is what the THCA flower trade was built on, and it is what Section 781 closes. The new text defines hemp by “a total tetrahydrocannabinols concentration (including tetrahydrocannabinolic acid) of not more than 0.3 percent on a dry weight basis” (P.L. 119-37).
States that count THCA already
As of Oct. 3, 2026, the state desk counts these states as applying a total-THC or post-decarboxylation test to hemp products, among others:
| State | How the state counts | Source |
|---|---|---|
| California | 0.3% total THC; hemp flower barred from retail since Jan. 1, 2026 | AB 8 (2025) |
| Colorado | Total THC after decarboxylation | SB 23-271 |
| Florida | “Total delta-9,” defined as delta-9 + 0.877 × THCA | Fla. Admin. Code r. 5K-4.034 |
| Georgia | Total-THC formula; flower barred at retail | SB 494 (2024), SB 33 (2026) |
| Minnesota | Flower over 0.3% total THC is cannabis | Minn. Stat. ch. 342 |
| New Mexico | Total-THC standard from Jan. 28, 2026 | 20.10.2 NMAC |
| New York | Total-THC math for cannabinoid hemp | OCM Part 114 |
| Oregon | Over 0.3% total THC not sellable to consumers | OLCC rules |
| Virginia | 0.3% total THC since 2023 | SB 903 |
| Wisconsin | Delta-9 “as tested using post-decarboxylation” | Wis. Stat. 94.55 |
| Wyoming | Total THC across all isomers | SF 32 (2024) |
Four states still define hemp by delta-9 alone, which keeps THCA flower in their hemp-retail lane until the federal date: Nebraska, North Carolina, Pennsylvania and South Carolina. Missouri uses a delta-9 test only until its own law moves intoxicating hemp to licensed dispensaries on Nov. 12. Every row, with its primary source, is in our state-by-state table.
What changes on a lab report on Dec. 11
Nothing about the lab work. Liquid-chromatography reports already list THCA and delta-9 separately, and most print a total. What changes is which line answers the legal question. Before Dec. 11 it was delta-9. From Dec. 11 it is total THC, on a dry-weight basis, against the same 0.3 percent limit.
Sources
- 7 U.S.C. 1639o, the hemp definition that governs THCA flower until Dec. 11, 2026
- 7 CFR part 990, USDA domestic hemp production program
- USDA AMS, Information for Hemp Testing Laboratories
- P.L. 119-37, sec. 781 and H.R. 6500
Reporting, not legal advice. Reviewed Oct. 3, 2026.
Questions readers asked
What is the total THC rule?
A test that counts THCA, at 87.7 percent of its weight, along with delta-9 THC. From Dec. 11, 2026, federal law defines hemp as no more than 0.3 percent total THC on a dry-weight basis, as of the law in force Oct. 3, 2026.
Has the USDA always tested hemp for total THC?
For growing crops, since its first hemp production rule in October 2019. Samples are taken within 30 days before harvest and must account for THCA. That rule governs fields, not finished products sold after harvest.
Do hemp labs have to be registered with the DEA?
7 CFR 990.3 says only DEA-registered labs may test crops after Dec. 31, 2022, but the USDA has delayed enforcing that requirement. As of Oct. 3, 2026, its posted notice delays enforcement until Dec. 31, 2026.
Which states already use total THC?
As of Oct. 3, 2026, many, including California, Colorado, Florida, Georgia, Minnesota, New York, Oregon, Virginia, Wisconsin and Wyoming. Nebraska, North Carolina, Pennsylvania and South Carolina still use a delta-9 test, and Missouri does until its own law takes effect Nov. 12.
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