Opens TreeMonkey on this number. Free, no sign-up, works offline.
The figure you'll see most often is that a mature tree absorbs about 22 kg of CO₂ a year — the Arbor Day Foundation's "more than 48 pounds", as the US Forest Service published it. TreeMonkey uses it to turn tonnes into trees: one tonne is about 45 tree-years.
Treat it as a picture, not a measurement. Real trees vary enormously with species, age, soil and climate. For the UK, Forest Research puts the average across all woodland ages and types at 5.6 tonnes of CO₂ per hectare per year, with the fastest-growing stands reaching about 37. Big old trees hold a great deal: a 220-year-old oak that Forest Research measured contained 4.9 tonnes of carbon — about 18 tonnes of CO₂, gathered over two centuries.
That's why planting is a slow way to deal with a tonne emitted today, and why TreeMonkey frames trees as a way to picture carbon, not an offset you can bank. Not emitting it in the first place is far quicker.
Source: Arbor Day Foundation figure as published by the US Forest Service (2015); Forest Research, Climate change and forest carbon factsheet (Morison & Matthews, 2023). Figures are illustrative UK equivalents.
Related reading
Frequently asked questions
Is 22 kg exact?
No — it’s a widely used rule of thumb for a mature tree, the Arbor Day Foundation’s 48 lb a year. Real absorption depends on species, age, site and management, so treat tree counts as illustrative.
How much CO₂ does a tree absorb in its lifetime?
Too much depends on the tree for one number. A 220-year-old oak measured by Forest Research held 4.9 tonnes of carbon — about 18 tonnes of CO₂ — but that is a big, old tree; most trees store far less over their lives.
How many trees does it take to absorb a tonne of CO₂?
About 45 mature trees working for a year, at 22 kg each — or around a fifth of a hectare of average UK woodland, which takes up 5.6 tonnes per hectare per year.