How we estimate a tree's lifetime CO₂
The CO₂ figure shown on each tree — for example "0.8 tonnes CO₂" — is our estimate of the carbon dioxide a tree is expected to absorb over its whole lifetime, not in a single year. It is a modelled estimate grounded in published forest science: an estimate with an uncertainty range, not a guarantee or an exact measurement.
What the number means
- Per tree, over its lifetime — the carbon a tree is expected to absorb across its functional lifespan (often several decades), not per year.
- An estimate with a range — modelled from real growth data and published equations; we work in ranges, not false precision.
- Conservative and survivorship-adjusted — not every seedling survives, and our field plots track that so the estimate reflects it.
- Varies by species, site and climate — which is why the figure differs between projects and countries.
How we calculate it
- Measure real growth. We run semi-random forest-inventory circle plots for survival, growth and density, track plantings with GPS and geotagged photos, and use drone and satellite monitoring of canopy growth where available. We plant native species suited to each site.
- Estimate biomass. We apply species-specific allometric equations from GlobAllomeTree (the FAO/CIRAD global database), using diameter at breast height (DBH) and height to estimate above-ground biomass, plus below-ground (root) biomass via standard IPCC root-to-shoot ratios.
- Convert biomass to carbon. Roughly 47–50% of a tree's dry biomass is carbon (species-specific where data exist), giving the carbon stored at each age.
- Convert carbon to CO₂. We multiply carbon by 3.67 (the molecular-weight ratio of CO₂ to carbon), then fit a growth curve across the species' expected lifespan to reach the lifetime CO₂ per tree.
How we keep it honest
- Uncertainty ranges — we run many scenarios (Monte Carlo), varying the equation, wood density, carbon fraction and growth model, and report ranges rather than a single false-precise number.
- Independent cross-checks — we compare our figures against independent allometric models and run sensitivity analyses on the assumptions that matter most.
- Reviewed and updated — estimates are refined as monitoring data accumulates for each project.
What this number is not
It is not a guarantee — forests face real-world risks. It is a complement to, not a replacement for, cutting your own emissions. And it is not the same as a verified carbon credit: for independently registered and retired credits, see our Verra (VCS) carbon credits and Gold Standard carbon credits.
Frequently asked questions
Is the figure per year or for the tree's whole life?
For the tree's whole life — the total CO₂ it is expected to absorb across its functional lifespan, not an annual figure.
Is it measured or modelled?
Modelled. We combine real growth data from field plots and remote sensing with published allometric equations. It is a scientifically grounded estimate, not an exact measurement.
How do you turn carbon into CO₂?
We multiply the carbon stored by 3.67, the molecular-weight ratio of carbon dioxide to carbon.
Do you account for trees that don't survive?
Yes. Our forest-inventory plots track survivorship, and that is reflected in the estimate.
Is buying a tree the same as buying a carbon credit?
No. Funding a tree supports planting or forest protection with an estimated lifetime CO₂ benefit. A verified carbon credit is a separately registered, audited and retired unit — see our Verra and Gold Standard pages.
Why does the CO₂ figure differ between countries?
Because carbon capture depends on species, age, size, climate and site conditions, which vary by project.
Reviewed by Evertreen. Last updated: June 2026.
Methods: species-specific allometric equations via GlobAllomeTree (FAO/CIRAD); biomass-to-carbon and root-to-shoot ratios per IPCC 2006 Guidelines (Vol. 4, AFOLU); carbon-to-CO₂ factor 3.67.
