Calorific Value (NCV/GCV)
Two engineers can compute the emissions from the exact same tonne of natural gas and arrive at answers roughly a tenth apart — not because either made an arithmetic error, but because they quietly used different definitions of how much energy that gas contains. The gap hides in a single word on the emission factor: “net” or “gross”.
That word is the calorific-value basis. Calorific value is the energy released when a fuel is burned — reported as either net (NCV) or gross (GCV), and getting the two mixed up is one of the most common errors in fuel accounting.
Calorific value is the energy released when a unit of fuel is fully combusted. Gross (GCV/HHV) counts the heat recovered when combustion water condenses; net (NCV/LHV) does not, so NCV is about 10% lower for natural gas. The factor and the calorific value must share a basis.
Definition — Energy Released on Combustion
Calorific value (CV), also called heating value, is the quantity of heat energy released when a specified amount of fuel is completely burned. It is what makes fuels comparable: it is measured in energy per unit of fuel — megajoules per kilogram (MJ/kg) for solids and liquids, or per cubic metre for gases, and often expressed in kWh for accounting. A fuel’s calorific value is the bridge between a physical quantity of fuel (litres, cubic metres, tonnes) and the energy it delivers, and therefore between fuel use and the emissions attributed to it.
The subtlety — and the reason this term needs a page of its own — is that calorific value is not a single number. Every fuel has two valid calorific values depending on one accounting choice: whether you count the energy locked up in the water vapour that combustion produces. That single choice defines the net-versus-gross distinction, and it quietly shapes every per-energy emission factor in a fuel inventory.
Definition at a glance
| What it is | Energy released when a unit of fuel is completely combusted |
|---|---|
| Also called | Heating value; units MJ/kg, MJ/m³, or kWh per unit |
| Two conventions | Gross (GCV / HHV) vs net (NCV / LHV) — differ by the water’s latent heat |
| Which is larger | Always GCV > NCV (gross includes heat net excludes) |
| Why it matters | Emission factors per unit energy depend on the basis — mix them and you err ~10% |
| Energy-content data | See the fuel calorific values dataset (DEFRA) |
Net vs Gross: The Latent-Heat Difference
When any hydrocarbon burns, its hydrogen combines with oxygen to form water. Turning that water from liquid to vapour absorbs energy — the latent heat of vaporisation. The two calorific values differ purely on whether that heat is counted as recoverable:
| Gross CV (GCV / HHV) | Net CV (NCV / LHV) | |
|---|---|---|
| Also known as | Higher heating value | Lower heating value |
| Water’s latent heat | Counted — assumes vapour condenses and the heat is recovered | Excluded — assumes water leaves as vapour |
| Relative size | Higher | Lower (always < GCV) |
| Reflects | A condensing appliance that recovers flue heat | A conventional appliance that vents hot flue gas |
| Typical gap | About 10% of gross for natural gas and about 5% for coal and oil (IPCC 2006); wider for wet fuels and for hydrogen | |
Two sources of water set the size of the gap. The first is the fuel’s hydrogen, which burns to water: the more hydrogen per unit of energy, the wider the gap, which is why natural gas (mostly methane) shows about 10% and hydrogen itself about 15%. The second is moisture already in the fuel, which also leaves the flue as vapour. A dry, hard coal behaves much like oil, but wet fuels such as wood chips or lignite lose more of their gross value, so the IPCC points inventory compilers to separate conversions for biomass rather than the 5% rule of thumb. Neither basis is right or wrong. What matters is consistency, as the next sections show with live values.
How to Convert GCV to NCV (and Back)
The conversion is a ratio, not a unit change: NCV = GCV × (NCV ÷ GCV), and GCV = NCV ÷ (NCV ÷ GCV). The ratio depends on the fuel. The IPCC 2006 Guidelines give the rule of thumb: for coal and oil the NCV is about 5% less than the GCV, and for most forms of natural and manufactured gas about 10% less. The table gives each fuel’s own figures from the UK Government’s 2026 fuel properties, read live from the data layer.
| Fuel | Gross CV GJ/tonne (= MJ/kg) | Net CV GJ/tonne (= MJ/kg) | Net ÷ gross |
|---|---|---|---|
| Natural gas | 49.521 | 44.695 | 0.903 |
| LPG | 49.333 | 45.944 | 0.931 |
| Petrol (average biofuel blend) | 45.374 | 42.976 | 0.947 |
| Diesel (average biofuel blend) | 45.581 | 42.869 | 0.941 |
| Gas oil | 45.286 | 42.569 | 0.940 |
| Fuel oil | 43.353 | 40.752 | 0.940 |
| Burning oil (kerosene) | 46.174 | 43.865 | 0.950 |
| Aviation turbine fuel | 46.215 | 43.905 | 0.950 |
| Coal (industrial) | 26.742 | 25.405 | 0.950 |
| Coal (domestic) | 30.119 | 28.613 | 0.950 |
| Hydrogen | 141.781 | 119.953 | 0.846 |
Two things in the table are worth knowing. First, several of the UK ratios come out at exactly 0.950 (coal, aviation turbine fuel, burning oil) or 0.940 (gas oil, fuel oil): for those fuels the published net value is a fixed fraction of the gross one, so converting with the ratio reproduces the official figure exactly. Second, hydrogen’s ratio of about 0.85 is the lowest of any common fuel. Its row is derived from NIST thermochemistry, because the UK table has no hydrogen; this is also why fuel-cell and electrolyser efficiencies are usually quoted against the lower (net) heating value.
When you know the fuel’s composition, you do not need a default ratio. The IPCC reproduces the ISO conversion for “as received” solid fuels, in MJ/kg:
Net CV = Gross CV − 0.212 H − 0.0245 M − 0.008 Y, where H is the percentage of hydrogen, M the percentage of moisture and Y the percentage of oxygen, all from the fuel’s ultimate analysis on an as-received basis.
The moisture term is why a wet fuel’s gap is larger: every percentage point of water costs 0.0245 MJ/kg on top of the water formed from hydrogen. A lab report that quotes both values is better than any formula. Use the formula when the report gives only gross, and a default ratio only when you have neither.
Why the Basis Matters: A Live Demonstration
Here is the counter-intuitive heart of the matter. Because an emission factor is emissions divided by energy, using the smaller (net) energy figure as the denominator produces a larger factor per kWh. The same fuel, burned identically, therefore carries a higher emission factor on an NCV basis than on a GCV basis. The live UK DEFRA factors for natural gas make it concrete:
| Fuel & basis | Emission factor kg CO₂e / kWh (live, DEFRA) |
|---|---|
| Natural gas — net CV (NCV) | 0.20199 |
| Natural gas — gross CV (GCV) | 0.18231 |
| LPG — net CV (NCV) | 0.23032 |
| LPG — gross CV (GCV) | 0.2145 |
For natural gas the NCV factor (0.20199 kg CO₂e/kWh [GreenCalculus fuels.gbr.natural_gas.kwh_ncv · DEFRA 2026 'Fuels'!D41 · v2026.284]) is about 11% higher than the GCV factor (0.18231 kg CO₂e/kWh [GreenCalculus fuels.gbr.natural_gas.kwh_gcv · DEFRA 2026 'Fuels'!D42]) — the same ~10% gap, now visible in the accounting. The trap follows directly:
A calorific value and an emission factor must always be paired on the same basis. If your gas meter reading is converted to energy on a gross basis (as UK billing is) but you apply a net-basis emission factor — or vice versa — your result is wrong by roughly a tenth, in whichever direction the mismatch runs. This is not a rounding issue; it is a systematic ~10% error that will not show up as an obvious mistake. Always check the “(Net CV)” or “(Gross CV)” label on the factor and match it to how the fuel’s energy was measured. The Scope 1 combustion calculator handles the basis internally; the fuel calorific values dataset gives the underlying energy contents.
Worked example: one UK gas bill, three answers
A site’s gas bill shows 10,000 kWh. UK suppliers calculate kWh on a gross basis, and DEFRA’s 2026 methodology says to use the gross factor by default unless the supplier states otherwise. With DEFRA’s 2026 factors (0.18231 kg CO₂e/kWh gross, 0.20199 net):
| Approach | Calculation | Result |
|---|---|---|
| Gross energy × gross factor (correct) | 10,000 × 0.18231 | 1,823 kg CO₂e |
| Convert to net, × net factor (also correct) | 10,000 × 0.9025 = 9,025 kWh net; × 0.20199 | 1,823 kg CO₂e |
| Gross energy × net factor (the mismatch) | 10,000 × 0.20199 | 2,020 kg CO₂e (+10.8%) |
The two consistent routes agree to the kilogram, because both describe the same gas. Only the mixed one is wrong, and nothing in the arithmetic warns you. Today’s values for each factor are in the table above. The 0.9025 is natural gas’s net-to-gross ratio from the conversion table.
The same discipline applies to every fuel. For reference, the live NCV-basis DEFRA factors span a wide range — natural gas at 0.20199 [GreenCalculus fuels.gbr.natural_gas.kwh_ncv], LPG at 0.23032 [GreenCalculus fuels.gbr.lpg.kwh_ncv · DEFRA 2026 'Fuels'!D37], diesel at 0.26071 [GreenCalculus fuels.gbr.diesel_average_biofuel_blend.kwh_ncv · DEFRA 2026 'Fuels'!D73], and industrial coal at 0.34223 kg CO₂e/kWh [GreenCalculus fuels.gbr.coal_industrial.kwh_ncv · DEFRA 2026 'Fuels'!D132] — but each must be applied to energy data measured on that same net basis.
Which Standard Uses Which Basis
Different regimes have settled on different conventions, which is exactly why the mismatch is so easy to make when working across sources:
| Regime / source | Basis |
|---|---|
| IPCC (national inventories, international convention) | Net (NCV / LHV) |
| UK DEFRA / DESNZ conversion factors | Both. Derived on a net basis from the UK inventory, then published per kWh on net and gross; gross is the default for UK gas in kWh |
| UK gas bills and UK energy statistics (DUKES) | Gross (GCV / HHV) |
| United States (EPA, 40 CFR Part 98 Table C-1 and common engineering practice) | Gross (HHV) |
| EU ETS monitoring and reporting | Net (NCV) |
The practical upshot: a UK company reading gas consumption from a bill (gross) must use a gross-basis factor, while a multinational rolling up sites against IPCC defaults (net) must convert consistently. Neither basis is “correct” — but crossing them silently is the error. DEFRA’s own methodology says its factors start on a net energy basis and are converted with gross and net calorific values, which is why every fuel appears in both columns. GreenCalculus carries both bases for each fuel so the pairing is explicit rather than assumed.
Which Energy Unit — MJ, kWh, GJ, Therms and BTU
Calorific value is quoted in whichever energy unit the source regime happens to favour, and that choice is regional and industrial rather than scientific. Solids and liquids usually appear as MJ/kg, gases as MJ/m³. UK corporate accounting works in kWh, and UK gas billing adds therms. US engineering data arrives as BTU/lb or MMBtu. Older and many Asian datasets still use kcal/kg, and IEA-style national aggregates roll everything up into tonnes of oil equivalent (toe). Same fuel, same energy, five different numbers on the page.
What matters about that list is what it is not. Moving between these units is exact arithmetic — a defined ratio, lossless in both directions, with no physics in it. Moving between net and gross is not: that is a real ~10% adjustment for the latent heat of the water combustion produces. A unit conversion never changes the basis, and a basis conversion is never merely a unit change. Most calorific-value errors are one of those two operations quietly doing the other’s job.
Exact conversion constants
| From | To | Multiply by |
|---|---|---|
| 1 kWh | MJ | 3.6 |
| 1 GJ | kWh | 277.78 |
| 1 GJ | MJ | 1,000 |
| 1 TJ | GJ | 1,000 |
| 1 therm | kWh | 29.3071 |
| 1 therm | MJ | 105.506 |
| 1 MMBtu | GJ | 1.05506 |
| 1 kWh | BTU | 3,412.14 |
| 1 toe | GJ | 41.868 |
| 1 kWh | kcal | 859.85 |
Only the first of those is exact by definition: one kilowatt-hour is 3.6 megajoules, because a watt is a joule per second. The rest are rounded, and two of them carry a trap worth naming.
The tonne of oil equivalent is a convention, not a measurement. 41.868 GJ is a defined constant, and no actual tonne of oil is obliged to match it — a toe figure therefore tells you about an aggregation rule, not about a fuel. And the calorie is ambiguous. The international-steam-table calorie is 4.1868 kJ, giving 859.85 kcal/kWh; the thermochemical calorie is 4.184 kJ, giving 860.42. The gap is small on one boiler and material on a national aggregate — and legacy kcal/kg datasets rarely state which one they used. When a source does not say, treat the basis of its calorie the same way you treat the basis of its calorific value: unstated is not the same as standard.
Quick converters: step the energy ladder with kWh to MJ, kWh to GJ, MJ to GJ and GJ to TJ; scale electrical quantities with kWh to MWh, MWh to GWh and GJ to MWh; cross into US and UK billing units with kWh to BTU, kWh to therms, therms to MJ and MMBtu to GJ; and handle legacy or aggregate bases with kWh to kcal and kWh to tonnes of oil equivalent. For the statistical aggregates that report fuel in equivalent terms, coal to oil equivalent handles the conversion.
Common Confusions
- Assuming a fuel has one calorific value. It has two — net and gross — differing by the latent heat of the water combustion produces. Always state which.
- Thinking the net-basis factor is “smaller”. The opposite: because the net energy denominator is smaller, the per-kWh emission factor on an NCV basis is larger than on a GCV basis for the same fuel.
- Mixing a gross energy reading with a net factor. UK gas bills are gross; IPCC factors are net. Cross them and you err ~10% — the single most common fuel-accounting slip.
- Confusing calorific value with the emission factor. Calorific value is energy per unit of fuel; the emission factor is emissions per unit of fuel or energy. Related, but not the same number.
- Treating “heating value”, HHV and GCV as different things. Higher heating value and gross calorific value are the same; lower heating value and net calorific value are the same. Only the terminology differs by region.
- Converting units and converting basis in one step. Moving kWh to GJ is exact arithmetic; moving gross to net is a ~10% physical adjustment. Do both at once and you cannot tell afterwards which one introduced the error — state each separately.
Frequently Asked Questions
Calorific value (also called heating value) is the amount of heat energy released when a unit of fuel is completely burned. It is measured in energy per unit of fuel — megajoules per kilogram or per cubic metre, and often kWh per unit in accounting — and it is what lets you convert a physical quantity of fuel into the energy it delivers and the emissions attributed to it. Crucially, every fuel has two calorific values, net and gross, depending on whether the energy in the water vapour formed during combustion is counted. That distinction is central to how fuel emission factors are defined.
The difference is the latent heat of the water produced when a fuel burns. Gross calorific value (GCV), also called higher heating value (HHV), counts the heat you would recover if that water vapour condensed back to liquid — as it does in a condensing boiler. Net calorific value (NCV), or lower heating value (LHV), excludes it, assuming the water leaves as vapour up the flue. Because gross counts extra recoverable heat, GCV is always higher than NCV. The gap is about 10% for natural gas, 5–6% for liquid fuels, and smaller for coal — largest for fuels with a high hydrogen content, since they make the most water. Both are valid; what matters is not mixing them.
Because emission factors are quoted per unit of energy, and energy depends on the basis. An emission factor is emissions divided by energy — so using the smaller net energy figure as the denominator gives a larger factor per kWh. For UK natural gas, the live DEFRA factor is 0.20199 kg CO₂e/kWh [GreenCalculus fuels.gbr.natural_gas.kwh_ncv] on a net basis versus 0.18231 [GreenCalculus fuels.gbr.natural_gas.kwh_gcv] on a gross basis — the net factor is about 11% higher. If you convert your fuel use to energy on one basis but apply a factor on the other, your emissions are wrong by roughly that 10%. The rule is simple: always pair the calorific value and the emission factor on the same basis, and check the “(Net CV)” or “(Gross CV)” label before you calculate.
UK energy data is mostly gross. UK gas bills convert the volume used to kWh on a gross calorific value (GCV/HHV) basis, and the UK’s energy statistics (DUKES) use gross values throughout. The DEFRA emission factors are published on both bases. They are derived on a net basis from the UK greenhouse gas inventory, and DEFRA’s methodology says to use the gross factor by default for natural gas in kWh unless your supplier states it used net. By contrast, the IPCC and most national inventories use net calorific value (NCV/LHV), as does much of continental Europe’s power-sector data, while the United States commonly uses gross (HHV). This divergence is precisely why cross-border or multi-source fuel accounting is error-prone: a UK company reading gross energy from a bill must use a gross factor, while the same fuel appearing in an IPCC-based inventory is on a net basis. GreenCalculus publishes both bases for each fuel so the pairing is explicit.
Yes — they are the same concepts under different names. Net calorific value (NCV) and lower heating value (LHV) are identical: both exclude the latent heat of the water vapour. Gross calorific value (GCV) and higher heating value (HHV) are also identical: both include it. “Calorific value” is more common in Europe and international standards; “heating value” is more common in the United States and engineering contexts. So NCV = LHV and GCV = HHV, and GCV/HHV is always the larger of the two. The only thing to watch is that a source states which it is using — the words change, but the ~10% difference for gas does not.
Multiply the gross value by the fuel’s net-to-gross ratio. For UK natural gas the ratio is 0.9025, so 10,000 kWh gross is about 9,025 kWh net; for diesel it is 0.941. To go the other way, divide by the same ratio. Without fuel-specific data, the IPCC rule of thumb is that NCV is about 5% below GCV for coal and oil and about 10% below for natural gas. With a lab analysis, the IPCC’s Box 1.1 formula subtracts 0.212 MJ/kg per percent hydrogen, 0.0245 per percent moisture and 0.008 per percent oxygen from the gross value. The units do not change: both values are in MJ/kg, GJ/tonne or kWh per unit of fuel.
Net calorific value (NCV), also called lower heating value (LHV), is the heat released when a unit of fuel burns completely, minus the heat needed to evaporate the water in the flue gas. That water comes from the fuel’s hydrogen and from any moisture in the fuel. It is the heat a boiler that vents its flue gas can actually use, so it is lower than the gross calorific value: about 10% lower for natural gas and about 5% for coal and oil. UK diesel, for example, has a net calorific value of 42.869 GJ per tonne [GreenCalculus fuel_properties.diesel.net_cv_gj_tonne · DEFRA 2026] against a gross value of 45.581 [GreenCalculus fuel_properties.diesel.gross_cv_gj_tonne · DEFRA 2026]. The IPCC Guidelines and the EU Emissions Trading System both work on a net basis.
Need someone who does this? 6 carbon accounting & inventory providers in our directory →