Carbon accounting articles describe each step separately, which makes it hard to see how a diameter measurement becomes a tonne of CO₂e and how much shrinks along the way. What follows is one calculation with every multiplier visible. The numbers are illustrative, chosen to be internally consistent and not from any real project.
The Chain
From tree to tonne
1. Measure
A stem at 24 cm DBH, height 14 m, wood density 0.55 g/cm³.
2. Apply allometry
The equation returns above-ground biomass for that stem, say 250 kg.
3. Add below-ground
Root:shoot ratio of 0.24 gives 60 kg of root biomass. Total 310 kg.
4. Convert to carbon
Multiply by the carbon fraction, 0.47 → 146 kg C.
5. Convert to CO2e
Multiply by 44/12 → 534 kg CO2e for this one tree.
That final multiplier, 44/12, roughly 3.67, is the molecular mass ratio of CO₂ to carbon, and it is the step that makes the numbers suddenly look large. A tonne of carbon is 3.67 tonnes of CO₂ equivalent.
Scaling to the Project
Now the same figure has to represent a landscape.
Suppose the plot is 500 m², contains 22 such stems, and totals 5.6 tonnes CO₂e. Expanding to a hectare means multiplying by 20, giving 112 tCO₂e/ha.
That expansion factor is where sampling error enters. The plot is a sample of the stratum, and the stratum mean carries a confidence interval. With 30 plots and moderate variability, a 90% confidence interval of ±12% on the mean would be unremarkable.
Then the Subtractions Begin
| Step | Value | Running total |
|---|---|---|
| Gross stock, project, year 10 | 112 tCO₂e/ha | 112 |
| Less baseline stock | −8 tCO₂e/ha | 104 |
| Less project emissions (fuel, fertiliser N₂O) | −6 tCO₂e/ha | 98 |
| Less leakage deduction | −4 tCO₂e/ha | 94 |
| Less uncertainty deduction (at ±12%) | −6 tCO₂e/ha | 88 |
| Less buffer pool contribution (non-permanence risk) | −13 tCO₂e/ha | 75 |
The gross figure was 112. The issuable figure is 75, which is about two thirds.
What the Table Shows
Two things worth sitting with.
The buffer pool is the largest single deduction. It is not a penalty; it is insurance against reversal, held at the registry and released if the project survives. It is also the deduction developers most often omit from early financial models, which is why those models overstate revenue by a wide margin.
The uncertainty deduction is the one you control. Baseline, project emissions and leakage are largely determined by the situation. The uncertainty deduction is determined by measurement design and at a wider interval, say ±25%, that line roughly doubles.
That is the concrete financial case for sampling design. Not precision for its own sake: the difference between ±12% and ±25% here is around 6 tCO₂e/ha, every year, for the life of the project.
The Caveat
Real methodologies differ in the order of operations, which pools are included, how leakage is treated and how the buffer is set. This example is a shape, not a template.
Its purpose is to make the compounding visible. Each multiplier is individually unremarkable; applied in sequence they turn a plot measurement into something roughly two-thirds its size, and a developer who has not run the arithmetic through to the end is usually modelling the first row.
Check the land before you commit
Eligibility turns on land history and forest cover at a cut-off date. TREEO Eligibility runs satellite-based forest cover detection on your area of interest, before a single seed goes into the ground.
