Fuel Heating Value Calculator (Dulong, HHV ⇄ LHV)

Understanding the fuel heating value calculator — concept and principle

The heating value tells you how much heat a kilogram of fuel releases when it burns completely. Using Dulong's formula and a fuel's elemental analysis, this calculator estimates the higher heating value (HHV) and the lower heating value (LHV) in MJ/kg.

Carbon supplies most of the heat; the water vapour formed takes 1.22 MJ/kg away as latent heat.

How it is calculated

HHV = 0.338 C + 1.442 (H − O/8) + 0.094 S, with C, H, O and S in weight percent (equivalent to 33.8, 144.2 and 9.4 MJ/kg for mass fractions).
LHV = HHV − 2.442 × (9 H/100 + w/100), where w is the moisture in weight percent.

2.442 MJ/kg is the latent heat of vaporisation of water at 25 °C, and the factor 9 converts hydrogen into the mass of water it forms (2 kg of H gives about 18 kg of H₂O).

The principle

Dulong treated a fuel as a mixture of its elements and added up their heats of combustion: roughly 33.8 MJ for each kilogram of carbon, 144 MJ for each kilogram of hydrogen and 9.4 MJ for each kilogram of sulphur. Oxygen in the fuel is assumed to be already bound to hydrogen as water, so one-eighth of the oxygen mass is subtracted from the hydrogen; only the remaining "available hydrogen" can burn. HHV counts the heat released when the water in the flue gas condenses, while LHV assumes that water leaves as vapour, so the latent heat of both the formed water and the fuel moisture is subtracted.

Worked example

Defaults: C = 75%, H = 5%, O = 8%, S = 1%, moisture = 5%.
Available hydrogen: 5 − 8/8 = 4%.
HHV = 0.338 × 75 + 1.442 × 4 + 0.094 × 1 = 25.35 + 5.768 + 0.094 = 31.212 MJ/kg.
Water in flue gas per kg fuel: 9 × 0.05 + 0.05 = 0.5 kg.
LHV = 31.212 − 2.442 × 0.5 = 31.212 − 1.221 = 29.991 MJ/kg.

Each point is the calculator re-run with only “Carbon (wt%)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Carbon (wt%)	HHV (MJ/kg)
18.8	12.1995
37.5	18.537
56.2	24.8745
75	31.212
93.8	37.5495
112	43.887
150	56.562

How to read the result

A value near 30 MJ/kg is typical of a good bituminous coal. Lignite and wood give much lower values because they contain more oxygen and moisture, while methane reaches about 55.5 MJ/kg HHV and 50 MJ/kg LHV because of its high hydrogen content. The gap between HHV and LHV grows with hydrogen and moisture. Boiler efficiencies quoted on an LHV basis look higher than the same boiler on an HHV basis, so always check which basis a figure uses.

Common mistakes

Mixing bases: C, H, O and S should be on the same basis (dry or as received) as the moisture you enter.
Counting the hydrogen and oxygen of the moisture twice, once in the ultimate analysis and again as w.
Using Dulong's formula for biomass or other oxygen-rich fuels, where its error is larger.

Keep in mind: Dulong's formula is an empirical estimate, usually within a few percent for coals but less reliable for other fuels. For contracts, emissions reporting or design, use a measured heating value from a bomb calorimeter.

Frequently asked questions

What is the difference between gross and net calorific value?

Gross calorific value is the HHV and net calorific value is the LHV; the names are used interchangeably.

Why is LHV used for engines and gas turbines?

Their exhaust is too hot for water to condense, so the latent heat is never recovered.

What happens to nitrogen and ash?

They release no heat, so they simply dilute the fuel and lower the heating value per kilogram.

Sources: Perry's Chemical Engineers' Handbook, section on fuels and combustion. McGraw-Hill. · Speight, J. G. Handbook of Coal Analysis. Wiley.

Checked 8 Nov 2026. Standard textbook formulas in SI units, computed in your browser. For learning and estimates — real designs must follow your local codes and be checked by a qualified engineer.

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