Direct answer: Delta-9-only testing measures just one cannabinoid against the 0.3% dry-weight threshold. Total-THC testing adds THCA to the equation — using the formula Delta-9 + (THCA × 0.877), which accounts for how much Delta-9 THC the THCA would become if decarboxylated. This single formula change is why so many current hemp flower products fail compliance under a total-THC standard even though they pass under Delta-9-only testing.
The Formula, in Plain Terms
The 0.877 conversion factor reflects the molecular weight lost when THCA loses its acid group during decarboxylation (heating). A product with 0.25% Delta-9 and 20% THCA would pass a Delta-9-only test easily, but its total THC would calculate to roughly 17.8% — wildly over any hemp threshold.
Who Already Uses Total-THC Testing
USDA's own compliance testing program for licensed hemp growers already uses total THC (post-decarboxylation) to determine whether a grower's crop is in compliance — it's the states' retail markets and the federal retail-product definition that have lagged behind, which is exactly what Section 781 changes starting November 12, 2026.
Why This Matters for Consumers, Not Just Growers
Once the federal retail standard shifts to total THC, most high-THCA hemp flower and many hemp-derived edibles built around the Delta-9-only loophole will no longer qualify as legal hemp — regardless of what state you're in.
FAQ
What is the 0.877 factor in total THC testing?
It's the conversion factor accounting for the mass lost when THCA converts to Delta-9 THC during decarboxylation (heating) — used to estimate a product's 'potential' Delta-9 content.
Does USDA already use total THC testing?
Yes, for compliance testing of licensed hemp growers' crops. The federal retail product definition is now catching up, effective November 12, 2026.
Will my state's testing standard change automatically?
Some states already use total-THC testing in their own statutes; others rely on the current federal Delta-9-only definition and will be directly affected when the federal standard shifts.