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An average UK petrol car emits about 0.264 kg CO₂e per mile (0.164 kg/km). Drive the UK average of roughly 7,400 miles a year and that's about 1.95 tonnes — which a mature broadleaf tree, absorbing ~21 kg a year, would take around 93 tree-years to soak up.
Two caveats worth being honest about. First, trees absorb slowly and over decades, so "planting to offset" is never a like-for-like swap for the emission you make today. Second, the far bigger lever is the car itself: fewer miles, or an electric car charged on an increasingly clean grid, cuts the number dramatically. Trees are the picture; reducing first is the plan.
Source: DESNZ/DEFRA GHG conversion factors (average petrol car) · Forest Research (tree absorption). Figures are illustrative UK equivalents.
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Frequently asked questions
Is planting trees a real offset?
Not directly. Trees lock up carbon slowly, over decades, and results vary hugely by species, site and survival. Treating a tree count as an illustration of scale is fair; treating it as a guaranteed offset is not — reducing the emission is always the stronger move.
What about an electric car?
An EV charged on the UK grid emits far less per mile than petrol, and falls further every year as the grid decarbonises. TreeMonkey lets you compare grid electricity against petrol directly.