Concepts, explained
The ideas behind the numbers — each written to be correct, compact and sourced. Read these to understand why some conversions are exact and others are only ever estimates.
What is energy?
Energy is the capacity to do work — one quantity, many units (joules, watt-hours, calories, BTU).
Read →kW vs kWh
kW is power (a rate); kWh is energy (a rate over time). You cannot convert one to the other without a duration.
Read →Joule vs watt-hour
Both measure energy. 1 Wh = 3600 J exactly, so 1 kWh = 3.6 MJ — a pure, exact identity.
Read →BTU and MMBTU
The British thermal unit and its million-fold multiple, common in US energy and gas markets.
Read →What is a therm?
A therm is 100,000 BTU — a billing unit for natural gas, defined by convention.
Read →What is a barrel?
The oil barrel is a volume unit: exactly 42 US gallons. Its energy content is a separate, estimated quantity.
Read →Barrel vs boe
A physical barrel is a volume; a “barrel of oil equivalent” (boe) is a fixed energy convention. They are not the same thing.
Read →toe and oil-equivalent units
toe, tce and boe are energy-equivalence conventions, exact by fiat — not measurements of any real oil or coal.
Read →HHV/GCV vs LHV/NCV
Higher heating value counts the heat of condensing water vapour; lower heating value does not. The gap can be 5–20%.
Read →Natural gas: m³ to kWh
Converting a cubic metre of gas to energy is never exact — it depends on composition and reference conditions.
Read →CO₂ vs CO₂e
CO₂ is only carbon dioxide; CO₂e bundles other greenhouse gases by their warming potential. There is no conversion between them.
Read →Why fuel conversions are approximate
Density, calorific value and emission factors are material properties that vary — so fuel results are sourced estimates, not constants.
Read →Why electricity emissions depend on region and year
A kWh of grid electricity has no single carbon factor — it depends on the country, the year and even the time of day.
Read →Food calories vs technical calories
A dietary “Calorie” is a kilocalorie — 1000 small calories. Confusing them is a factor-1000 error.
Read →