Energy statistics often express everything "in oil terms" or "in coal terms" so that gas, electricity, coal and oil can be added up on one scale. The units that do this — toe, tce and boe — are energy-equivalence conventions. They are exact by definition, but they are not properties of any real barrel, tonne of oil, or tonne of coal.
The definitions
- toe (tonne of oil equivalent):
1 toe = 41.868 GJ— the IEA/OECD convention. - tce (tonne of coal equivalent):
1 tce = 29.3076 GJ. - boe (barrel of oil equivalent):
1 boe = 5.8 MMBTU ≈ 6.1 GJ(the US "5.8 MMBTU convention"; see barrel vs boe).
From the first two you get the exact relation 1 toe = 1.428571… tce. The tool marks all of these as standard definition: the arithmetic is exact, but each unit stands for a convention, not a measured property.
Exact by fiat, not by nature
The toe was fixed historically from a net calorific value of about ten million kilocalories, but that origin is now just a round number in a definition. No real tonne of oil is guaranteed to hold exactly 41.868 GJ, and no real tonne of coal exactly 29.3076 GJ — actual fuels vary. The convention deliberately freezes a single figure so that international energy balances are consistent and comparable. That is its purpose and also its limitation.
Equivalence units versus real fuel
Because these are conventions, the tool treats them very differently from the energy content of a physical fuel. Converting toe, tce or boe to gigajoules is exact. But asking how much energy is in an actual tonne of a specific coal, or an actual barrel of a specific crude, is a sourced estimate that varies with grade and moisture — a different question with a different, hedged answer. The tool never presents the energy-equivalence convention as if it were a measurement of the real fuel, and always labels which convention a result uses.