What GCV measures
Gross calorific value (GCV) is the amount of heat released when a unit of coal is fully burned, expressed in kilocalories per kilogram (kcal/kg). It is the closest single proxy for the useful energy in a tonne of coal, which is why it is the number that most directly drives price.
Domestic thermal coal in India is commonly traded in the GCV 3,500–5,000 kcal/kg range. Higher GCV means more heat per tonne — and usually a higher price per tonne.
Why the reporting basis matters
The same coal can show different GCV numbers depending on the moisture basis used for the measurement, so always compare like with like:
- ARB (as-received basis) — measured with the moisture the coal arrives with; closest to what you actually fire.
- ADB (air-dried basis) — measured after standard air drying; reads higher than ARB.
- GAR / NAR — gross vs net as-received; NAR subtracts the energy lost vaporising moisture.
GCV, ash and moisture together
GCV does not live alone. High ash and high moisture both pull usable energy down and add handling and disposal cost, so a headline GCV should always be read alongside the ash and moisture for the same sample.
A consignment quoted on one basis but delivered on another can look like a bargain on paper and underperform at the boiler. The defence is a documented certificate for the lot you are buying.
Verifying the number you pay for
Because GCV prices the coal, it is worth verifying independently rather than taking it on trust. Third-party laboratory GCV verification on a representative sample, with the sample retained, lets either side settle a later question against physical evidence.
Frequently asked
- What does GCV 4,500 mean?
- It means the coal releases about 4,500 kilocalories of heat per kilogram when fully burned. Higher GCV indicates more energy per tonne, which typically commands a higher price.
- What is the difference between GAR and ADB?
- GAR (gross as-received) is measured with the moisture the coal arrives with; ADB (air-dried basis) is measured after standard air drying and reads higher. Always compare quotes on the same basis.
- Why does ash content matter if GCV is high?
- Ash is non-combustible — it lowers usable energy and adds handling and disposal cost. Read GCV alongside ash and moisture from the same sample for a true picture.