What the 0.3% THC Legal Limit Actually Means
Under the 2018 Agriculture Improvement Act (the Farm Bill), “hemp” is Cannabis sativa L. with a delta-9 THC concentration of no more than 0.3% on a dry-weight basis. Anything above that is “marijuana” under federal law.
USDA rules add an “acceptable hemp THC level” that accounts for measurement uncertainty in lab results. If the lab’s uncertainty range includes 0.3% or less, the sample can be considered compliant.
- Hemp definition: ≤ 0.3% delta-9 THC by dry weight
- Testing: Post-decarboxylation (often called “total THC”)
- Compliance: Includes lab measurement uncertainty (MU)
Why 0.3%? It traces back to a 1970s botanical paper by Ernest Small as a way to distinguish hemp and drug-type cannabis. It wasn’t meant as a pharmacological “safe” level, but it became the global benchmark.
How Labs Measure THC (Delta-9 vs. “Total THC”)
Most compliance tests look at “total THC,” which estimates the THC that would exist after heating (decarboxylation). Labs commonly calculate:
Total THC = Δ9-THC + 0.877 × THCA
This avoids undercounting THCA in raw plant material. Many states and the USDA require high-performance liquid chromatography (HPLC) or equivalent validated methods, and results include MU.
- Delta-9 THC: The primary intoxicating compound
- THCA: Acidic precursor that converts to THC with heat
- MU: A statistical range showing test uncertainty
Tip: Check whether a Certificate of Analysis (COA) reports both Δ9-THC and THCA and clearly labels “Total THC.” That’s what regulators usually look at for the hemp threshold.
THC Legal Limit for Plants vs. Finished Products
For crops, the federal limit is straightforward: ≤ 0.3% delta-9 THC by dry weight. For finished products, it’s more nuanced.
- Plant material: Tested before harvest; crops above the limit are “hot.”
- Finished goods: Many states apply the 0.3% threshold to the total product weight. Some now impose milligram caps per serving and per package.
- Delta-8 and other isomers: Regulated state-by-state; federal rules are evolving.
Example: A 5-gram gummy may legally contain up to 15 mg delta-9 THC by weight (0.3% of 5,000 mg) in some jurisdictions, even though it can feel intoxicating. Always check state-specific rules.
Step-by-Step: How to Check If a Product Meets the 0.3% Rule
- Find the COA. Scan the QR code or link on the label; verify the batch number matches your product.
- Confirm the lab. Prefer DEA-registered or accredited labs as required in your state; check test date and method (HPLC or equivalent).
- Locate “Total THC.” Look for delta-9 THC and THCA; confirm how “total THC” is calculated.
- Check units. For tinctures, “mg/mL”; for edibles, “mg per serving” and “per package”; for flower, “% by dry weight.”
- Do the math. For edibles: 0.3% × product weight (mg) = maximum mg delta-9 allowed by weight-based rules.
- Review MU. If the MU range includes 0.3% or less, it may be compliant for hemp under USDA rules.
- Verify state rules. Some states limit mg per serving/package beyond the 0.3% calculation.
Real-Life Example: A “Hot” Crop That Passed on Remediation
A small Kentucky grower sampled late in the season. The first test reported 0.36% total THC (MU ±0.07). Because the MU range included 0.3%, the crop remained eligible for remediation.
They removed high-THC floral material, remediated the biomass, and retested. The second COA came back at 0.25% total THC. They harvested within the state’s window and sold the compliant biomass to a CBD extractor.
Takeaway: Sampling timing, MU, and remediation options can make or break compliance.
Common Mistakes That Push THC Above the Limit
- Late harvests, especially after hot, sunny weeks
- Plant stress (drought, pests) increasing cannabinoid synthesis
- Inconsistent sampling across a field or lot
- Poor storage that concentrates cannabinoids (water loss raises percentage)
- Confusing delta-9 THC with total THC on COAs
Regulatory Snapshot and Key Sources
At the federal level, the 0.3% THC definition of hemp stems from the 2018 Farm Bill, with testing and enforcement outlined in USDA’s final rule (7 CFR part 990). The FDA has not set THC limits for foods/supplements nationally, so states fill the gap with product rules.
- USDA Hemp Program: ams.usda.gov/rules-regulations/hemp
- 2018 Farm Bill text: congress.gov
- State law finder: Check your state department of agriculture or health
Note: This article is for information only and is not legal advice. Consult local regulators or counsel for your situation.
THC Legal Limit FAQs
What does the 0.3% THC limit really mean?
It’s the legal boundary between hemp and marijuana in the U.S. If the delta-9 THC concentration (often measured as total THC) is 0.3% or less by dry weight, it’s hemp. Labs include measurement uncertainty when determining compliance.
Does the 0.3% rule apply to edibles and tinctures?
Often yes, but states vary. Some apply 0.3% by total product weight, while others set milligram caps per serving and per package. Always check your state’s rules for finished goods.
How do I read a COA to verify compliance?
Match the batch number, find “Total THC,” and confirm the testing method. For edibles, compare the mg of THC per serving/package to your state’s limits. For flower, verify total THC percentage is ≤ 0.3% or within MU.
What happens if a crop tests above 0.3%?
It’s considered a “hot” crop. Depending on your state, you may be allowed to remediate (e.g., remove flowers or process to biomass) and retest. Otherwise, disposal may be required under supervision.
Is 0.3% a safety threshold for consumers?
No. The 0.3% number is a legal line, not a pharmacological safety standard. Products under 0.3% by weight can still contain intoxicating milligrams of THC if the item is large or concentrated.
Conclusion
The 0.3% rule defines hemp under federal law, but real-world compliance depends on total THC, measurement uncertainty, and state-specific product rules. Always verify COAs, do the math on thc content, and document your process.