Under federal law, delta-9 THC is the psychoactive cannabinoid whose concentration draws the line between legal hemp and illegal marijuana. The threshold is 0.3% on a dry weight basis: cannabis at or below that level is hemp and sits outside the Controlled Substances Act, while anything above it is marijuana. That has been the federal legal definition of delta-9 THC’s regulatory role since the Agriculture Improvement Act of 2018, and it holds until November 12, 2026, when a new law replaces the delta-9-only measurement with total THC and caps finished cannabinoid products at 0.4 milligrams per container.
The 0.3% Rule in the Statute
The definition lives in 7 U.S.C. § 1639o. Hemp means the plant Cannabis sativa L. and any part of it, including seeds, extracts, cannabinoids, and derivatives, so long as the delta-9 THC concentration does not exceed 0.3% on a dry weight basis.1Office of the Law Revision Counsel. 7 U.S.C. 1639o – Definitions The Controlled Substances Act then carves hemp out of the definitions of “marihuana” and “marijuana” at 21 U.S.C. § 802(16)(B), pulling it off Schedule I entirely.2Office of the Law Revision Counsel. 21 U.S.C. 802 – Definitions
The reclassification treats hemp as an agricultural commodity under USDA oversight. Producers must operate under either a USDA-approved state or tribal plan or directly under the USDA’s hemp production program.3eCFR. 7 CFR Part 990 Subpart C – USDA Hemp Production Plan States may impose rules stricter than the federal floor.4Office of the Law Revision Counsel. 7 U.S.C. 1639p – State and Tribal Plans Cannabis grown outside these frameworks, or above 0.3% delta-9 THC, falls back under the CSA.
How the 0.3% Is Measured
Two technical rules shape whether a sample passes: it is measured dry, and the number reported is not raw delta-9 alone but “total THC” after decarboxylation.
Dry Weight Basis
Labs remove moisture before measuring cannabinoid content, typically drying samples to between 5% and 12% moisture before grinding and analysis.5Agricultural Marketing Service. Laboratory Testing Guidelines U.S. Domestic Hemp Production Program Water content shifts with humidity, harvest timing, and storage, so measuring wet material would produce inconsistent results and allow growers to dilute the THC percentage on paper.
Total THC and the 0.877 Multiplier
Raw cannabis carries little delta-9 THC. Most of what will become delta-9 exists as THCA, a non-psychoactive acid that converts to delta-9 THC when heated. Because smoking, vaping, or cooking triggers that conversion, federal rules require labs to report a total THC value that captures the conversion potential.6eCFR. 7 CFR Part 990 – Domestic Hemp Production Program
The formula is total THC = delta-9 THC + (0.877 × THCA). The 0.877 multiplier reflects the molecular weight lost when THCA sheds its carboxyl group during decarboxylation.6eCFR. 7 CFR Part 990 – Domestic Hemp Production Program A crop with barely detectable delta-9 can still fail if its THCA content pushes the combined total above 0.3%.
Measurement of Uncertainty
No lab produces a perfectly exact reading, so labs must report a measurement of uncertainty alongside the result. If 0.3% falls anywhere within that range, the lot passes. A sample testing at 0.35% with an uncertainty of ±0.06 produces a range of 0.29% to 0.41%, and because 0.3% sits inside that range, the crop qualifies as hemp.7Federal Register. Establishment of a Domestic Hemp Production Program
Sampling Window and Labs
A sampling agent must collect samples no more than 30 days before the anticipated harvest.8Agricultural Marketing Service. Frequently Asked Questions (FAQ) THC levels tend to climb as plants mature, so testing too early can produce a passing number that misstates harvest potency. Federal rules require testing at DEA-registered laboratories, but the USDA has repeatedly delayed enforcement of that requirement; non-DEA-registered labs may perform the testing through December 31, 2026.9Agricultural Marketing Service. USDA Extends Enforcement Deadline for Hemp to Be Tested by DEA-Registered Laboratories
Why the Percentage Behaves Differently in Finished Products
Pegging legality to a percentage of dry weight keeps potency low in raw plant material, but the math changes for heavy finished products. A 5-gram gummy at 0.3% delta-9 THC by dry weight can legally contain about 15 milligrams of delta-9 THC, comparable to a full recreational dose in a state-legal dispensary. A 100-gram chocolate bar could hold roughly 300 milligrams and still fit the definition.
This is the core reason a national market for hemp-derived delta-9 edibles grew after 2018, often in states where marijuana remained fully illegal. The FDA has said the dry weight calculation has “limited utility” for finished products and for intermediates like extracts and tinctures, and warned that processed products can exceed 0.3% delta-9 by dry weight even when the starting material qualified as hemp.10U.S. Food and Drug Administration. Cannabis and Cannabis-Derived Compounds – Quality Considerations for Clinical Research
What Changes on November 12, 2026
Congress passed P.L. 119-37 in November 2025. On November 12, 2026, it rewrites the federal hemp definition and closes most of the gaps that emerged after 2018.11Congressional Research Service. Change to Federal Definition of Hemp and Implications for Federal Law
The core shift: the threshold moves from delta-9 THC alone to total THC concentration. Under the current definition, a product can contain unlimited THCA, delta-8 THC, or other intoxicating cannabinoids as long as delta-9 stays below 0.3%. The new definition measures all THC-type compounds together.11Congressional Research Service. Change to Federal Definition of Hemp and Implications for Federal Law
The new law also carves out specific exclusions from the hemp definition:
- Finished hemp-derived cannabinoid products containing more than 0.4 milligrams of total THC per container, regardless of the concentration percentage.
- Hemp-derived intermediates such as extracts, concentrates, and distillates that exceed 0.3% total THC concentration.
- Products containing cannabinoids that cannot be naturally produced by the cannabis plant, or that were synthesized outside the plant.
- Seeds from cannabis plants exceeding 0.3% total THC concentration.
The 0.4-milligram-per-container cap effectively ends the dry weight loophole for edibles. A gummy that could previously hold 15 milligrams of delta-9 THC under the percentage rule will be limited to less than half a milligram per container. The FDA is directed to further define “container” and to publish lists of naturally occurring cannabinoids, THC-class cannabinoids, and cannabinoids with similar effects.11Congressional Research Service. Change to Federal Definition of Hemp and Implications for Federal Law Industrial hemp grown for fiber, grain, or seed-oil remains explicitly included.
When a Crop Tests Above 0.3%
Federal regulations separate negligent violations from intentional ones, and the dividing line sits at 1.0% total THC on a dry weight basis.
Between 0.3% and 1.0%: Negligence, No Criminal Penalty
A grower whose crop tests above 0.3% but at or below 1.0% total THC, and who made reasonable efforts to grow compliant hemp, is treated as having committed a negligent violation. Negligent violations carry no criminal penalties at any level of government.12eCFR. 7 CFR 990.6 – Violations of State and Tribal Plans The producer follows a corrective action plan and reports compliance to the state or tribal authority for at least two years.
The crop itself still cannot be sold. Non-compliant plants must be disposed of through methods approved under the state or USDA plan, generally by plowing under, composting, or burning. Three negligent violations within a five-year period disqualifies the producer from growing hemp for five years from the date of the third violation.12eCFR. 7 CFR 990.6 – Violations of State and Tribal Plans
Above 1.0%: Marijuana Under the CSA
Once a crop clears 1.0% total THC, the violation is no longer presumed negligent, and the matter may be referred to law enforcement. The cannabis is legally marijuana under the Controlled Substances Act. Federal mandatory minimums can reach five years for 100 or more plants and ten years to life for 1,000 or more, with enhanced penalties for repeat offenses. Prosecutors rarely pursue farmers whose crops drifted slightly over 1.0% because of genetics or weather, but the exposure exists for producers who repeatedly or intentionally grow high-THC varieties without proper licensing.
What the Threshold Does Not Decide
Meeting the 0.3% rule does not make a product FDA-compliant. The FDA treats both THC and CBD as excluded from the definition of “dietary supplement” because they were first studied as active drug ingredients, and adding either to food is prohibited absent an FDA regulation, which the agency has not issued.13U.S. Food and Drug Administration. FDA Regulation of Cannabis and Cannabis-Derived Products, Including Cannabidiol (CBD) Products marketed to diagnose, cure, mitigate, treat, or prevent disease are treated as unapproved drugs and draw warning letters regardless of THC content.14U.S. Food and Drug Administration. FDA Issues Warning Letters to Companies Illegally Selling CBD and Delta-8 THC Products
Marijuana’s separate rescheduling also does not alter the hemp definition. In 2026, the Justice Department placed FDA-approved marijuana products and products regulated under state medical marijuana licenses in Schedule III, and a broader rulemaking to reclassify marijuana from Schedule I to Schedule III is ongoing, with a hearing scheduled to begin June 29, 2026.15U.S. Department of Justice. Justice Department Places FDA-Approved Marijuana Products and Products Containing Marijuana Regulated by a State Medical Marijuana License in Schedule III The 0.3% threshold, shifting to total THC in November 2026, still determines whether cannabis qualifies as hemp in the first place.