# Doubling time

> The days an unchecked pest population needs to double, equal to ln 2 divided by r_m (0.693 / r_m).

- Canonical: https://genetixbay.com/knowledge/glossary/doubling-time.html
- Also written: population doubling time
- Glossary category: Pests and diseases · 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"

Doubling time is the time a population growing at its intrinsic rate of increase takes to double: 0.693 divided by r_m. An r_m of 0.2 per day gives 3.5 days; 0.35 per day gives 2 days. It is the most intuitive way to explain why a week of inaction matters.

## In practice

Doubling time is an upper bound from lab conditions; real rooms with predators or poor food run slower. Even so, a pest that doubles every 3 days goes up about 128-fold in 3 weeks (seven doublings), which is why weekly scouting is the minimum.

## Don't confuse with

- **Generation time**: birth to next birth, several doublings long.

## Related terms

[Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md)

## Read more

- [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md)

## Sources

1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605