THCA → Total THC calculator
Enter the THCA and Δ9-THC percentages from any certificate of analysis (COA) to get the total THC figure — the number that decides federal hemp compliance — and see instantly whether the sample is under the 0.3% limit.
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Enter values above — total THC%, hemp compliance, and mg dosage 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. The federal definition of hemp is based on 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) Hemp-compliant when Total THC ≤ 0.3% of dry weight
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. Reading the total-THC line on a certificate of analysis is the only reliable way to know what you're buying.
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. This is the figure used to determine federal hemp compliance.
What is the legal THC limit for hemp?
Federally, hemp must contain no more than 0.3% total THC by dry weight. Because total THC counts decarboxylated THCA, high-THCA flower can exceed 0.3% total THC even when its Δ9-THC reads low on a COA.
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 sold and on your state's law. Many states follow the federal 0.3% total-THC dry-weight definition; some regulate THCA directly. Always check your local rules and the product's certificate of analysis (COA).
Shopping for THCA you can verify?
Every batch The Leaf Concierge carries ships with a scannable COA — so you can run these exact numbers yourself. Same-day delivery across Miami, nationwide shipping.
Educational tool only — not legal advice. Cannabinoid laws vary by state and change frequently. Verify your local regulations and the product's certificate of analysis before purchase. 21+.