# How do I turn the gross calorific value on my coal lab report into net calorific value using moisture, hydrogen and oxygen?

Canonical: https://senseible.earth/answers/coal-gross-to-net-calorific-value-formula

The Intergovernmental Panel on Climate Change (IPCC) Box 1.1 gives, in megajoules per kilogram (MJ/kg) as received: net calorific value (NCV) = gross calorific value (GCV) minus 0.212 times hydrogen percent, minus 0.0245 times moisture percent, minus 0.008 times oxygen percent. Take all three from the ultimate analysis, as received.

## The formula and its units

- Box 1.1, Conversion between gross and net calorific values: Net CV = Gross CV minus 0.212 H minus 0.0245 M minus 0.008 Y, in MJ/kg, where M is percent moisture, H is percent hydrogen and Y is percent oxygen.
- The box says these come from the ultimate analysis, as received, which includes total moisture. It credits the World Coal Institute as its source.
- 1 MJ/kg = 1 gigajoule (GJ) per tonne, as the box states. Many Indian reports give kilocalories (kcal) per kg. IPCC's own coal thresholds, 23,865 kilojoules per kilogram (kg) and 5,700 kcal per kg, imply 4.1868 kilojoules per kcal.
- Enter percentages as printed, 3.0 for 3.0%, not 0.03.

## Formula or the 5% shortcut

- IPCC's text says that for coal and oil the NCV is about 5 percent less than the GCV, and for most natural and manufactured gas about 10 percent less. It offers Box 1.1 as the algorithm when moisture, hydrogen and oxygen are known.
- The formula can land above or below 5%. Wet or hydrogen-rich fuel loses more. Dry, low-hydrogen fuel loses less.

## How this differs from the lignite answer on this site

- That answer uses a shorter form, GCV minus 0.212 times hydrogen minus 0.0244 times moisture, with no oxygen term, and calls it approximate.
- Against Box 1.1 the moisture coefficient differs by 0.0001 per percent, which is 0.0045 MJ/kg at 45% moisture. The missing oxygen term is 0.008 MJ/kg per percent, so 0.12 MJ/kg at 15% oxygen.
- Both are small beside the gap between GCV and NCV. If your report prints oxygen, use Box 1.1 as IPCC prints it.
- Ask your lab whether its hydrogen figure includes the hydrogen in the moisture. The box does not say.

## 100 tonnes of coal, example report values

- Report (example values): GCV 4,200 kcal per kg, moisture 12%, hydrogen 3.0%, oxygen 9%, all as received
- GCV: 4,200 x 4.1868 / 1,000 = 17.585 MJ per kg
- NCV: 17.585 minus (0.212 x 3.0 = 0.636) minus (0.0245 x 12 = 0.294) minus (0.008 x 9 = 0.072) = 16.583 MJ per kg
- NCV / GCV = 0.943, so 5.7% below, against the 5% shortcut's 16.705
- Energy: 100 t x 16.583 = 1,658.3 GJ. At 94.6 kg of carbon dioxide (CO2) per GJ, the IPCC other bituminous default: 156,871 kg, 156.9 t CO2
- With the 5% shortcut: 1,670.5 GJ x 94.6 = 158,032 kg, 158.0 t, which is 0.7% higher

The report values are examples. Check which IPCC coal line fits your coal before choosing 94.6; the coal-lines answer on this site lists the thresholds.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. The coal lab report is a separate paper, so keep it beside the records and note which heat value basis you used.

- [GCV or NCV for coal, gas and oil](https://senseible.earth/answers/gcv-vs-ncv-in-fuel-emission-calculation)
- [Lignite emission factor in India](https://senseible.earth/answers/lignite-emission-factor-india)
- [Indian coal emissions from GCV](https://senseible.earth/answers/indian-coal-emissions-by-gcv)
- [Coal as received or air dried](https://senseible.earth/answers/coal-as-received-vs-air-dried-basis)

Sources: [IPCC 2006 Guidelines, Volume 2, Chapter 1 (section 1.4.1.2, Box 1.1, Table 1.1 coal definitions)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-11-05. Ask the lab which basis and which hydrogen figure its report prints before applying the formula.