# Total THC

> Total THC is a calculated figure, Δ9-THC plus 0.877 × THCA, estimating the maximum THC a sample could yield after full decarboxylation.

- Canonical: https://genetixbay.com/knowledge/glossary/total-thc.html
- Also written: total THC calculation, THC total, max THC, THCmax, total potential THC, 0.877
- Glossary category: Lab testing · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Total THC is not measured directly. The lab measures [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and [Δ9-THC](https://genetixbay.com/knowledge/glossary/thc.md) separately, usually by [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), then combines them, applying 0.877 to the THCA because [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) removes [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and about 12.3% of the molecule's mass. It is the figure most labels and legal limits use.

## In practice

A [COA](https://genetixbay.com/knowledge/glossary/coa.md) shows THCA 22.0% and Δ9-THC 0.8% w/w. Total THC = 0.8 + 0.877 × 22.0 = 0.8 + 19.3 = 20.1%. Adding the two lines without the factor (22.8%) inflates the figure by about 2.7 points, a common error or trick. Real-world conversion during smoking or cooking is lower than the theoretical total because of losses.

## Units and formula

Total THC (% w/w) = Δ9-THC + 0.877 × THCA. The factor is the molecular weight ratio, 314.5 / 358.5. Some rules define it differently (for example, also counting other THC isomers); check the definition the lab applied.

## Don't confuse with

- **THCA**: one input to the calculation.
- **Total cannabinoids**: all measured [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), not only THC.

## Myth check

House position: most flower people believe tests in the mid-20s to 30s really tests mid-teens to low 20s. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md).

## Related terms

[THCA](https://genetixbay.com/knowledge/glossary/thca.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md), [Total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md)

## Read more

- [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)

## Sources

1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271.
2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396