Under federal law, a cannabis crop qualifies as hemp only if its total THC concentration is 0.3% or less on a dry-weight basis. The total THC federal standard for hemp counts both the delta-9 THC already present in the plant and the THCA that would convert into delta-9 THC when heated. Cross that line, and the crop is no longer an agricultural commodity; it meets the Controlled Substances Act definition of marijuana.
How Total THC Is Calculated
Most of the THC in a living hemp plant isn’t delta-9 THC at all. It’s THCA, a non-psychoactive acid that only becomes delta-9 THC through decarboxylation, a chemical reaction triggered by heat or prolonged light. Because THCA-rich material can turn psychoactive after processing, federal regulations require testing labs to use post-decarboxylation or a similarly reliable method that captures both the delta-9 THC already there and the THCA that could convert into it.1eCFR. 7 CFR 990.3 – State and Tribal Plans; Plan Requirements
The formula is straightforward: Total THC = delta-9 THC + (THCA × 0.877). The 0.877 factor reflects the molecular weight lost when THCA sheds its carboxyl group during decarboxylation. Run the math on a sample containing 0.10% delta-9 THC and 0.30% THCA and you get 0.10 + (0.30 × 0.877) = 0.363%. The raw delta-9 reading looked safe. The crop still fails.
The 0.3% Threshold and the Measurement of Uncertainty
Federal law defines hemp as Cannabis sativa L. with a total tetrahydrocannabinols concentration, including THCA, of not more than 0.3% on a dry-weight basis.2Office of the Law Revision Counsel. 7 USC 1639o – Definitions That single number separates legal hemp from a Schedule I substance.
No lab instrument is perfectly precise, so USDA regulations build in a statistical buffer called the measurement of uncertainty. Every test result carries a plus-or-minus value reflecting the equipment’s precision. The reported total THC plus or minus that value creates a range, and if 0.3% falls anywhere within that range, the crop passes. The USDA calls this the “acceptable hemp THC level.”3eCFR. 7 CFR 990.1 – Meaning of Terms
Here’s what that looks like in practice. A lab reports 0.35% total THC with a measurement of uncertainty of ±0.06%. The resulting range is 0.29% to 0.41%. Because 0.3% sits inside that range, the crop is compliant despite the raw number exceeding the baseline. If the reported concentration were high enough that even the bottom of the uncertainty range sat above 0.3%, the sample would fail.
How the Statute Caught Up with the Testing Rule
The 2018 Farm Bill originally defined hemp using a “delta-9 tetrahydrocannabinol” threshold, which created a gap between the statute’s language and the USDA’s total-THC testing regulations. Congress closed that gap through the FY2026 agriculture appropriations act (P.L. 119-37), enacted November 12, 2025, which rewrote the statutory definition to explicitly reference “total tetrahydrocannabinols concentration (including tetrahydrocannabinolic acid).”2Office of the Law Revision Counsel. 7 USC 1639o – Definitions The statute and the testing protocol now say the same thing.
The same law added exclusions that reshape the downstream product market, effective November 12, 2026. Synthetic or manufactured cannabinoids fall outside the hemp definition, as do intermediate hemp-derived cannabinoid products sold directly to consumers as final products, and any final product containing more than 0.4 mg combined total of THC (including THCA) and other cannabinoids with similar effects.2Office of the Law Revision Counsel. 7 USC 1639o – Definitions Those exclusions affect manufacturers of finished cannabinoid products more than growers of raw hemp flower, but the effective date matters for anyone in the downstream supply chain.
Pre-Harvest Sampling
The 0.3% number gets applied to a specific slice of plant material collected at a specific moment. A state, tribal, or federal sampling agent physically collects the sample no more than 30 days before the anticipated harvest, and the crop must be harvested within 30 days of collection. Miss that window and a new sample has to be pulled before harvest can proceed.4eCFR. 7 CFR Part 990 Subpart C – USDA Hemp Production Plan – Section 990.24
The agent cuts the top five to eight inches from the main stem of selected plants, targeting the flowering tops where cannabinoid concentrations are highest. The number of plants sampled scales with lot size: at least one for lots under an acre, a USDA scaling chart for one to ten acres, and Codex Alimentarius methodology for anything larger.5USDA Agricultural Marketing Service. Sampling Guidelines for Hemp Individual cuttings from across the lot combine into a single composite sample. The protocol has to ensure, at a 95% confidence level, that the plants in the lot will not exceed 0.3%.
A “lot” for these purposes is a contiguous area in a field, greenhouse, or indoor facility containing the same variety or strain throughout. Samples from separate lots stay separate and never combine, because each lot gets its own compliance determination.
Some states and tribes offer performance-based sampling, an alternative that reduces the sampling burden on low-risk producers using factors like seed certification and compliance history. Any such protocol has to be built into the state or tribal plan approved by USDA, and it still has to meet a 95% confidence level that no more than 1% of plants in each lot will exceed the acceptable hemp THC level.6Agricultural Marketing Service. Commonly Asked Questions About Performance-Based Sampling
Laboratory Testing and the Certificate of Analysis
The USDA’s final rule requires hemp samples to be tested by laboratories registered with the Drug Enforcement Administration. The agency has repeatedly delayed enforcement of that requirement because of a shortage of DEA-registered labs with adequate capacity. The current enforcement deadline is December 31, 2026, so non-DEA-registered labs can still conduct hemp testing through the end of the year.7Agricultural Marketing Service. USDA Extends Enforcement Deadline for Hemp to Be Tested by DEA-Registered Laboratories USDA strongly encourages ISO/IEC 17025 accreditation but does not require it at the federal level.8Agricultural Marketing Service. Laboratory Testing Guidelines – U.S. Domestic Hemp Production Program
Every lab report shows the total delta-9 THC concentration on a dry-weight basis along with the measurement of uncertainty. Those two figures let anyone reviewing the document calculate whether the crop meets the acceptable hemp THC level. Without a valid certificate of analysis, the plant material lacks the documentation needed for lawful interstate transport or sale.
What Happens When a Crop Exceeds 0.3%
Failing the test doesn’t automatically mean the crop is lost or the producer is punished. Federal rules draw a second line at 1.0% total THC. A producer whose crop exceeds 0.3% but stays at or below 1.0%, and who can show reasonable efforts to grow compliant hemp, does not commit a negligent violation.9Federal Register. Establishment of a Domestic Hemp Production Program The crop still has to be remediated or destroyed, but the producer’s license record stays clean.
A producer with a non-compliant lot can choose one of two remediation paths. The first is to strip all flowers, buds, trichomes, trim, and kief from the stalks, leaves, and seeds and destroy the floral material, keeping the remaining plant material labeled “hemp for remediation purposes” and separate from compliant lots. Seeds removed during this process cannot be used for planting. The second option is to shred the entire lot into a homogenous blend of all plant parts, then store and label the resulting biomass as “hemp for remediation purposes.”10USDA Agricultural Marketing Service. Hemp Remediation and Disposal Guidelines Either way, the producer notifies USDA of the intent to remediate, and the material must be resampled and retested to confirm total THC now falls within the acceptable level.11eCFR. 7 CFR Part 990 Subpart C – USDA Hemp Production Plan – Section 990.27 If the biomass fails retesting, it must be destroyed. Approved on-farm disposal methods include plowing under, mulching, composting, disking, bush mowing, deep burial, and burning.
Crops above 1.0% total THC, or cases where the producer cannot show good-faith efforts at compliance, trigger a Notice of Violation. The producer must submit a corrective action plan that details the steps to fix the problem and demonstrate future compliance, and that plan stays in effect for at least two years.12GovInfo. 7 CFR 990.31 – Violations Three negligent violations within a five-year period result in license revocation and a five-year bar on growing hemp, running from the date of the third violation.13eCFR. 7 CFR Part 990 Subpart C – USDA Hemp Production Plan – Section 990.29 Producers are limited to one negligent violation per calendar year, so a single disastrous season cannot consume multiple strikes at once.9Federal Register. Establishment of a Domestic Hemp Production Program