The 3-30-300 rule: what its author says and what two studies reported
The 3-30-300 guideline asks for three trees in view from every home, 30 percent tree canopy in every neighbourhood and a park or green space within 300 metres. This page gives the rule as its author describes it and the results two published studies reported.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page attributes every claim to the named paper. It does not say whether the rule is right for a given city, and it does not recommend a canopy target. The tools that measure canopy are on the i-Tree tools page.
The rule, as its author wrote it
Cecil Konijnendijk, of the Nature Based Solutions Institute, introduced the rule in a July 2021 article for the Biophilic Cities Journal and set it out in a 2023 paper in the Journal of Forestry Research. The 2023 abstract describes it as a guideline for urban forestry that aims to give equitable access to trees and green spaces. The thresholds it gives are three well-established trees in view from each home, school and workplace, a canopy of 30 percent or more in each neighbourhood, and a public green space within 300 m of each residence.
- 3: in the 2021 article the first element is that every citizen should be able to see at least three trees of a decent size from their home. The article notes that the Danish municipality of Frederiksberg has a tree policy calling for every citizen to see at least one tree from their home.
- 30: the article says the work of Thomas Astell-Burt and colleagues in Australia has repeatedly found 30 percent to be an important threshold. It says Barcelona, Bristol, Canberra, Seattle and Vancouver had set a target of 30 percent canopy cover, and that where trees struggle to grow, as in arid climates, the target should be 30 percent of vegetation.
- 300: the article says the European Regional Office of the World Health Organization recommends a maximum distance of 300 metres to the nearest green space of at least 1 hectare, and that where that is hard to retrofit a decent size of 0.5 hectares should be a minimum.
The article places the rule beside Frank Santamour's 10-20-30 diversity rule, which it states as no species above 10 percent, no genus above 20 percent and no family above 30 percent of an urban forest. It says the 10-20-30 rule does not focus on the benefits urban forests provide, which is the gap 3-30-300 is meant to fill. Species mix is on the street tree diversity page.
What published studies reported
| Study, place and sample | What the authors reported |
|---|---|
| Nieuwenhuijsen and colleagues, Environmental Research, December 2022. Barcelona, Spain; 3,145 people aged 15 to 97 in the Barcelona Health Survey 2016 to 2017 | Only 4.7 percent met a surrogate version of the rule. Meeting the full surrogate rule pointed the same way on mental health, medication use and psychologist or psychiatrist visits, but the abstract reports statistical significance only for the last of these (odds ratio 0.31, 95 percent confidence interval 0.11 to 0.91). Surrounding greenness was significantly linked to better mental health; tree window view and access to a major green space were not. |
| Helbich and colleagues, Environment International, August 2025. The Netherlands; 180,949 survey respondents in 2022 | 16.4 percent met the rule. Those who met it were less likely to be overweight and more likely to be physically active, both reported as significant. Neither the rule nor its components were linked to the other health or behaviour outcomes tested, and the authors call the role in mental health inconclusive. |
The Barcelona authors call their measure a surrogate: they built the three indicators from questionnaire, GIS, remote sensing and land cover map data.
How the rule is measured
A 2024 paper in Science of the Total Environment by Browning and a group of coauthors, including Konijnendijk, reviewed ways to measure the rule by expert consensus. It describes seven kinds of data and processes: vegetation indices, street level analyses, tree inventories, questionnaires, window view analyses, land cover maps and green space maps. For the 3 component it recommends surveys and window-view analyses, for the 30 component high-resolution land cover maps, and for the 300 component green space maps combined with network analyses. Inventories are described on the tree inventories page.
Sources
- Konijnendijk, The 3-30-300 Rule for Urban Forestry and Greener Cities, Biophilic Cities Journal, July 2021, copy hosted by the University of Toronto, read October 9, 2026
- Konijnendijk, Evidence-based guidelines for greener, healthier, more resilient neighbourhoods: Introducing the 3-30-300 rule, Journal of Forestry Research, 2023, abstract read on Europe PMC October 9, 2026
- Nieuwenhuijsen and colleagues, The evaluation of the 3-30-300 green space rule and mental health, Environmental Research, December 2022, abstract read on Europe PMC October 9, 2026
- Helbich and colleagues, Adherence to the 3+30+300 urban green space rule in the Netherlands, Environment International, August 2025, abstract read on Europe PMC October 9, 2026
- Browning and colleagues, Measuring the 3-30-300 rule to help cities meet nature access thresholds, Science of the Total Environment, January 2024, abstract read on Europe PMC October 9, 2026