# Chemotype ratio

> The chemotype ratio is the balance of a plant's main cannabinoids, usually THC to CBD, classing plants as type I (THC-dominant), II (mixed), III (CBD-dominant), IV (CBG) or V (near-zero).

- Canonical: https://genetixbay.com/knowledge/glossary/chemotype-ratio.html
- Also written: THC:CBD ratio, THC to CBD ratio, cannabinoid ratio, chemotype I II III, type I/II/III, CBD:THC ratio
- Glossary category: Cannabinoids and terpenes · 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"

The chemotype ratio describes how a plant's [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) output is split, almost always expressed as total [THC](https://genetixbay.com/knowledge/glossary/thc.md) to total [CBD](https://genetixbay.com/knowledge/glossary/cbd.md). Researchers use five broad classes: type I, THC-dominant; type II, mixed THC and CBD; type III, CBD-dominant; type IV, CBG-dominant; type V, almost no cannabinoids. The ratio is set mainly by the synthase genes, so it is highly heritable and stable within a clone.

## In practice

A COA showing total THC 21% and total CBD 0.05% is type I (ratio over 100:1). One showing 7% THC and 9% CBD is type II (about 1:1.3). Breeders crossing types I and III expect type II [F1s](https://genetixbay.com/knowledge/glossary/f1.md) and a [segregating](https://genetixbay.com/knowledge/glossary/segregation.md) [F2](https://genetixbay.com/knowledge/glossary/f2.md). Seedling genotyping can predict the class early; the absolute percentage still depends on many other genes and the grow.

## Don't confuse with

- **[Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md)** (genetics term): the overall chemical phenotype or class; the ratio is how it's measured.
- **Terpene profile**: aroma chemistry, separate from the cannabinoid ratio.
- **Potency**: total amount, independent of the ratio.

## Myth check

Indica/sativa labels don't predict the chemotype ratio or [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) (house position, supported by Smith et al. 2022 and others). See [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md).

## Related terms

[Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md)

## Read more

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

## Sources

1. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966
2. Hazekamp A, Fischedick JT. 2012. Cannabis: from cultivar to chemovar. Drug Testing and Analysis 4(7-8):660-667. https://doi.org/10.1002/dta.407
3. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363