THCA → Total THC calculator
Enter the THCA and Δ9-THC percentages from any certificate of analysis (COA) to get the total THC figure and compare it with the 0.3% limit. Add the container's net weight to compare total THC in milligrams with the 0.4 mg per-container cap.
Based on Public Law 119-37 section 781 and Public Law 119-103 section 2019 (full effect December 11, 2026); last verified . Sources and methodology.
Try a real-world example
Enter values above — total THC %, the 0.3% comparison, and (with a container weight) total mg against the 0.4 mg cap appear instantly.
How this calculator works
When cannabis flower is heated, THCA loses a carboxyl group and converts into THC, shedding mass as CO₂. Because of that mass loss, one percentage point of THCA does not become a full point of THC — it becomes about 0.877 of one. Public Law 119-37 section 781 defines hemp by total THC, which accounts for that conversion:
Total THC (%) = (THCA% × 0.877) + Δ9-THC%
0.877 = molar mass of THC (314.46) ÷ molar mass of THCA (358.47)
Limit: Total THC ≤ 0.3% of dry weight
Cap: total THC in a final product ≤ 0.4 mg per container
(total mg = Total THC % × 10 mg/g × grams in the container)This matters because high-THCA flower can read well under 0.3% Δ9-THC on its own, yet exceed 0.3% total THC once the THCA is counted. Read the total-THC line on the certificate of analysis, and see the dated summary of the 2026 federal changes for what applies from November 12, 2026 and December 11, 2026.
Read the full calculator methodology — the decarboxylation assumptions, edge cases, and the limits of the 0.877 factor.
Frequently asked questions
How do you calculate total THC from THCA?
Total THC (%) = (THCA% × 0.877) + Δ9-THC%. The 0.877 factor accounts for the mass lost as CO₂ when THCA decarboxylates into THC under heat. USDA's hemp production rule (7 CFR 990.1) and Florida's rule 5K-4.034(2)(q) use this formula, and Public Law 119-37 section 781 counts THCA in the federal hemp definition.
What is the federal THC limit for hemp?
The 2018 Farm Bill text still codified in 7 U.S.C. 1639o sets 0.3% delta-9 THC by dry weight. Public Law 119-37 section 781 replaces it with 0.3% total tetrahydrocannabinols including THCA, effective November 12, 2026 for one narrow class of cannabinoids and December 11, 2026 for the rest, per Public Law 119-103 section 2019. High-THCA flower can read low on Δ9-THC yet be far over 0.3% total THC.
What is the 0.4 mg per-container cap?
Section 781 excludes final hemp-derived cannabinoid products with more than 0.4 milligrams combined total per container of total THC (including THCA) and other cannabinoids with similar effects. Enter the container's net weight and this calculator multiplies total THC % × 10 mg per gram × grams, then compares the result with 0.4 mg. It counts THC and THCA only; the statute also counts other cannabinoids with similar effects. The full definition applies from December 11, 2026.
Why is THCA multiplied by 0.877?
THCA loses a carboxyl group (mass) when it converts to THC. The molar-mass ratio of THC to THCA is 314.46 / 358.47 ≈ 0.877, so each percentage point of THCA yields about 0.877 percentage points of THC after decarboxylation.
Does a high total-THC reading mean the flower is illegal?
It depends on how the product is classified and on your state's law. Florida's rule 5K-4.034 uses total THC with a 0.3% limit for hemp intended for human consumption; other states differ. Check your state's rules and the product's certificate of analysis (COA). This tool is information only, not legal advice.
What changes on December 11, 2026?
A plain-language summary of Public Law 119-37 section 781 and Public Law 119-103 section 2019, with links to the official text and a last-verified date.
Information only — not legal advice. Cannabinoid laws vary by state and change frequently. Verify your local regulations and the product's certificate of analysis. Last verified October 1, 2026.