# Total CBD

> Total CBD is a calculated figure, CBD plus 0.877 × CBDA, estimating the maximum CBD a sample could yield after full decarboxylation.

- Canonical: https://genetixbay.com/knowledge/glossary/total-cbd.html
- Also written: total CBD calculation, CBD total, max CBD, CBDmax, total potential CBD
- 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 CBD is calculated the same way as total [THC](https://genetixbay.com/knowledge/glossary/thc.md). The lab measures [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) separately and combines them, multiplying CBDA by [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) to account for the CO2 lost on decarboxylation. [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and CBDA are isomers, so the conversion factor is identical.

## In practice

A hemp-type COA reports CBDA 11.5% and CBD 0.4% w/w. Total CBD = 0.4 + 0.877 × 11.5 = 0.4 + 10.1 = 10.5%. Breeders use total CBD alongside total THC to place a plant in its chemotype class: the same plant's total THC might read 0.4%, giving a [CBD:THC ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) of about 26:1, a type III plant.

For anyone working under a hemp THC limit, the important number is usually total THC, not total CBD. A high-CBD plant still makes some THCA, because [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) isn't perfectly specific.

## Units and formula

Total CBD (% w/w) = CBD + 0.877 × CBDA. Factor = 314.5 / 358.5 (molecular weights of CBD and CBDA).

## Don't confuse with

- **CBDA**: one input to the calculation, not the total.
- **Total cannabinoids**: the sum of all measured [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md).
- **CBD content on a product label**: may be per serving or per container, not % w/w.

## Related terms

[CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md)

## Read more

- [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.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.