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, and like any such estimate it carries uncertainty: it is 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, not a measurement — modelled from growth data and published equations, so the actual figure for a given tree or site can be higher or lower.
- Varies with survival — not every seedling survives, and survival varies by site and year.
- Varies by species, site and climate — which is why the figure differs between projects and countries.
How we calculate it
- Monitor the plantings. Monitoring is carried out with our planting partners and varies by site and partner: depending on the project it can include survival and growth checks in sample plots, GPS-tracked plantings with geotagged photos, and drone or satellite imagery of canopy growth. Species are chosen with each partner to suit the site.
- Estimate biomass. We use published allometric equations from GlobAllomeTree (the FAO/CIRAD global database), species-specific where one exists and otherwise a general equation for the forest type, 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).
- Convert carbon to CO₂. We multiply carbon by 3.67 (the molecular-weight ratio of CO₂ to carbon) to reach the lifetime CO₂ per tree.
CO₂ absorbed to date
Alongside the lifetime estimate, our homepage shows a CO₂-absorbed-to-date figure. For each tree we take its tree model’s lifetime estimate and multiply it by the share of that model’s expected lifetime that has passed since the tree was funded, capped at the full lifetime; the site-wide figure is the sum across all trees. It is a straight-line allocation: real trees absorb slowly while young and faster as they grow, so in the early years it runs ahead of actual growth and later behind it. It is an indicator of progress over time, not a field measurement.
Until August 2026 this figure applied a single figure of 0.022 tonnes to every tree; it is now calculated per tree model as described above.
Uncertainty and updates
- Uncertainty — each per-tree figure is a single modelled estimate. The equation chosen, wood density, carbon fraction, survival and growth rate all affect it, so the true value for a given tree or site can be higher or lower.
- Updated as evidence changes — when new information, including a project’s monitoring data where it exists, shows a tree model’s figure should change, we change it and recalculate the site-wide totals and the customer forest pages that use it.
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. Each tree model’s per-tree figure is estimated with published allometric equations; individual trees are not measured. It is an 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?
Survival varies by site and species, and how it is monitored varies by site and planting partner. The per-tree figure is a modelled lifetime estimate, not a count of surviving trees.
Is buying a tree the same as buying a carbon credit?
No. Funding a tree supports tree planting, with an estimated lifetime CO₂ benefit. A certified carbon credit is a separate product: a registered unit retired on its project’s registry — 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.
How is the CO₂ absorbed-to-date figure calculated?
For each tree we take its tree model’s lifetime estimate and multiply it by the share of that model’s expected lifetime that has passed since the tree was funded, capped at the full lifetime. It is a straight-line allocation: an indicator of progress over time, not a field measurement. Our homepage shows it next to the lifetime estimate it comes from.
Reviewed by Evertreen. Last updated: September 2026.
Methods: allometric equations, species-specific where available, 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.
