IMO uses a carbon conversion factor of 3.206 tonnes of CO₂ for each tonne of diesel or gas oil consumed. It is a useful operational factor, but it is not the same thing as a full well-to-wake greenhouse-gas footprint.
For marine diesel and gas oil, the International Maritime Organization uses a carbon conversion factor, or CF, of 3.206 tonnes of CO₂ for every tonne of fuel consumed. The number appears in IMO energy-efficiency guidance and is based on the carbon content of ISO 8217 diesel/gas-oil grades DMX through DMB.
The calculation is deliberately simple when fuel consumption is already known by mass. A yacht that burns 10 tonnes of qualifying diesel or gas oil is associated with 32.06 tonnes of CO₂ under this factor, while 100 tonnes of fuel corresponds to 320.6 tonnes of CO₂.
Why one tonne of fuel produces more than one tonne of CO₂
The result can initially look impossible because the mass of CO₂ is much greater than the mass of fuel. Combustion explains the difference: carbon in the fuel combines with oxygen drawn from the atmosphere, and that oxygen becomes part of the mass of the carbon dioxide leaving the exhaust.
IMO’s 2022 EEDI calculation guidelines list diesel/gas oil with a lower calorific value of 42,700 kJ/kg, carbon content of 0.8744 and CF of 3.206 t-CO₂/t-fuel. The same table gives different factors for other fuels, including 3.151 for light fuel oil, 3.114 for heavy fuel oil and 2.750 for LNG, reflecting differences in carbon content and fuel chemistry.
How to use the factor on a superyacht
The cleanest calculation uses verified fuel mass from bunker records, tank measurements or a fuel-monitoring system: fuel consumed in tonnes multiplied by 3.206 equals tonnes of CO₂. If the yacht records fuel in litres, the volume first has to be converted to mass using an appropriate density for the actual fuel rather than assuming that every litre of marine diesel has identical mass.
The factor can be applied to main-engine and generator consumption, which matters on a superyacht because hotel loads can make auxiliary generation a significant part of annual fuel use. A serious yacht carbon account should therefore capture propulsion fuel and generator fuel rather than estimating emissions only from miles travelled.
What the 3.206 factor does not measure
The 3.206 figure is fundamentally a CO₂ conversion based on the carbon in the fuel used on board. It does not by itself represent all upstream emissions from extracting crude oil, refining the product, transporting it to the bunker location or supplying it to the yacht, and it is not a complete lifecycle CO₂-equivalent figure covering every greenhouse gas.
That distinction is becoming increasingly important because IMO’s lifecycle framework assesses fuels on a well-to-wake basis, combining well-to-tank and tank-to-wake emissions and accounting for greenhouse gases including CO₂, methane and nitrous oxide. A simple bunker-consumption calculation remains useful, but it answers a narrower question than a full lifecycle assessment.
The regulatory picture is still moving
IMO approved a proposed Net-Zero Framework in 2025 that would use lifecycle greenhouse-gas fuel intensity, but formal adoption was adjourned and negotiations are continuing through 2026. As of September 2026, the draft framework has therefore not replaced the established 3.206 CO₂ conversion factor used in existing energy-efficiency and fuel-consumption calculations.
For superyacht owners and managers, the practical lesson is to label the number correctly. Multiplying diesel or gas-oil consumption by 3.206 gives a defensible IMO-based estimate of direct fuel-related CO₂, but it should not be presented as the yacht’s complete climate footprint unless construction, electricity, refrigerants, shore power, tenders, aviation and the upstream fuel chain have also been addressed.
