Measurement
Carbon fraction
Carbon fraction is the share of dry biomass that is carbon by weight. It is the step that converts tonnes of wood into tonnes of carbon, which is then converted again into tonnes of carbon dioxide, the unit a carbon credit is counted in.
Methodologies publish a default value, and species specific laboratory values can replace it where they exist. A report should state which was used and where it came from.
The conversion from carbon to carbon dioxide is a fixed ratio of molecular weights, so the uncertainty sits in the biomass estimate and the fraction, not in that last step.