Δ⁹-THC Compliance: The 2018 Farm Bill 0.3 % Calculation

What does the 2018 Farm Bill actually say?

The Agriculture Improvement Act of 2018 (commonly called the 2018 Farm Bill) legalized hemp as a federal agricultural commodity. Hemp is defined as Cannabis sativa with a delta-9 tetrahydrocannabinol (Δ⁹-THC) concentration of not more than 0.3 % on a dry-weight basis. Anything above that threshold is marijuana, which remains Schedule I under federal law.

The 0.3 % number applies to total THC, not just the Δ⁹-THC measurement on its own. Total THC accounts for the decarboxylation that happens when raw cannabis is heated, dried, or metabolized.

The total-THC calculation

Cannabis plants produce tetrahydrocannabinolic acid (THCA) as the precursor to Δ⁹-THC. THCA itself is non-psychoactive but converts to Δ⁹-THC through decarboxylation — a loss of CO₂ that happens at temperatures above ~110 °C (during smoking, vaping, baking, or extraction).

The mass loss from CO₂ removal is the source of the conversion factor:

Total THC = (THCA × 0.877) + Δ⁹-THC

The 0.877 factor accounts for the molecular weight difference between THCA (358.5 g/mol) and Δ⁹-THC (314.5 g/mol). When THCA decarboxylates, it loses CO₂ (44 g/mol), so the mass conversion is:

314.5 / 358.5 = 0.8773

Rounded to 0.877, which is the conversion factor written into USDA rules and state-level hemp programs.

Why the calculation matters in COA work

A typical hemp / CBD product COA will report several different numbers:

• Δ⁹-THC % — the measured amount of decarboxylated Δ⁹-THC at the time of testing.
• THCA % — the measured amount of the acid precursor.
• Total THC % — the calculated post-decarb value, i.e. what the product would test at if the THCA had fully converted to Δ⁹-THC.

The regulatory line at 0.3 % applies to total THC, not to Δ⁹-THC measured directly. A product can have very low Δ⁹-THC (say, 0.1 %) and high THCA (say, 0.5 %), and its total THC would compute as:

(0.5 × 0.877) + 0.1 = 0.539 %

That's above the 0.3 % ceiling. The product is legally marijuana, not hemp — even though Δ⁹-THC alone is below 0.3 %.

Where COA disputes happen

Most disputes around hemp / CBD compliance come down to one of these issues:

• Δ⁹-THC reported without total THC. A COA that only reports Δ⁹-THC at 0.2 % might still represent a non-compliant product if THCA is high. Federal and state hemp programs require the total THC calculation.
• HPLC vs GC method differences. GC methods decarboxylate THCA to Δ⁹-THC during analysis, so the GC result is effectively "total THC" already. HPLC methods quantify THCA and Δ⁹-THC separately and require the post-decarb calculation. Both can be valid; the COA should explicitly state which method was used.
• Dry-weight vs as-received basis. The 0.3 % ceiling applies to dry-weight. A high-moisture sample tested as-received might appear under 0.3 %, but on a dry-weight basis the value is higher. Karl Fischer moisture or loss-on-drying needs to be reported with the THC value for unambiguous compliance.
• USDA vs state-level enforcement. The USDA's interim final rule applies to hemp production at the farm level. Once hemp is processed into finished products (CBD isolate, distillate, gummies, tinctures), state-level frameworks take over. The 0.3 % line is consistent across most state programs but the testing methodology and reporting format can vary.

The signed attestation

For brokers and carriers shipping hemp products across state lines, a signed Δ⁹-THC compliance attestation on the COA is the document they ask for. The attestation explicitly states that the product meets the 2018 Farm Bill total-THC threshold, lists the measurements that support it, and is signed by the analyst.

Our standard Δ⁹-THC compliance attestation includes:

• The HPLC method used (typically reverse-phase C18, 228 nm).
• The measured Δ⁹-THC % (dry-weight basis).
• The measured THCA % (dry-weight basis).
• The calculated total THC % per the (THCA × 0.877) + Δ⁹-THC formula.
• The result vs the 0.3 % ceiling, explicit pass / fail.
• The moisture content used in the dry-weight correction.
• The analyst signature, accession number, date issued.

Why isolate is easier than distillate

The Farm Bill compliance question is much easier for CBD isolate than for CBD distillate or broad-spectrum products:

• CBD isolate — ≥ 99 % pure CBD, with both Δ⁹-THC and THCA at or near detection limit. Total THC effectively zero. Compliance is unambiguous.
• Broad-spectrum distillate — typically 80-95 % CBD with minor cannabinoids retained. Δ⁹-THC is sometimes measurable; THCA may be measurable; total THC needs the calculation to be reported. Sometimes compliant, sometimes not.
• Full-spectrum hemp extract — retains all cannabinoids including THCA and Δ⁹-THC. Total THC compliance is the central question on every lot.

What about Δ⁸-THC?

The 2018 Farm Bill specifically references Δ⁹-THC, not Δ⁸-THC. This opened the door to Δ⁸-THC products marketed under the federal hemp framework. Several states have since regulated Δ⁸-THC separately; the FDA has issued guidance discouraging Δ⁸-THC products without full safety evaluation. The 0.3 % Δ⁹-THC ceiling does not apply to Δ⁸-THC content, but Δ⁸-THC products carry their own state-level regulatory exposure that's worth COA-documenting separately.

Our 16-cannabinoid panel quantifies Δ⁸-THC alongside Δ⁹-THC, THCV, CBG, CBN, and the rest of the cannabinoid family — providing the full profile rather than just the regulated-compound number.

Summary

The 2018 Farm Bill 0.3 % ceiling applies to total THC, not Δ⁹-THC alone. Total THC = (THCA × 0.877) + Δ⁹-THC, where the 0.877 factor accounts for the mass loss from decarboxylation. A compliance COA should report Δ⁹-THC, THCA, and total THC as separate numbers on a dry-weight basis, plus a signed analyst attestation tying the result to the Farm Bill compliance line. CBD isolate clears the compliance question easily; distillate and full-spectrum products require careful per-lot testing.

See our CBD isolate testing page for the signed Δ⁹-THC compliance attestation, or CBD & hemp testing overview for the full 16-cannabinoid panel and broader regulatory scope.