Tree Offset Calculator
How many trees it takes to absorb a given amount of carbon dioxide, and how long they need — with the caveats that make the number less comforting than it looks.
A mature broadleaf tree absorbs roughly 21 kg of CO₂ a year, though the figure varies enormously with species, climate, age and spacing.
How the tree offset calculator works
A mature broadleaf tree absorbs roughly 21 kg of CO₂ a year, though the figure varies enormously with species, climate, age and spacing. A newly planted sapling absorbs almost nothing for its first years, which is why "trees planted" and "carbon absorbed" are very different claims.
The arithmetic here is deliberately literal: this many trees, absorbing at this rate, take this long. It is not a statement that planting them cancels an emission. Carbon in a tree is released again if it burns, is felled or dies, while carbon released from fossil fuel is a permanent addition to the active carbon cycle — the two are not equivalent stores.
Formula: trees = CO₂ ÷ (absorption per tree per year × years)
Worked examples
| Inputs | Trees needed | Note |
|---|---|---|
| One tonne of CO₂ in a year | 47.6 | 47.6 trees |
| The same tonne over ten years | 4.8 | 4.8 trees |
| A long-haul return flight | 142.9 | 143 trees for a year |
FAQFrequently asked questions
How much CO₂ does a tree absorb?
A mature broadleaf absorbs roughly 21 kg a year, but it varies enormously with species, climate and age.
How many trees offset a tonne of carbon?
About 48 mature trees for a year, or five trees over ten years.
Do saplings count?
Barely at first. A newly planted tree absorbs very little for several years, which is why "trees planted" and "carbon absorbed" are different claims.
Is planting trees the same as not emitting?
No. Carbon in a tree returns to the air if it burns or is felled, while fossil carbon released is a permanent addition to the active carbon cycle.
How much land do they need?
At typical spacing about 1,600 trees fit in a hectare, so 48 trees need roughly 300 square metres.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- Australian Government — National Greenhouse Accounts Factors — the official Australian emission factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.