Gas unit converter: m³ ↔ kWh ↔ therms ↔ MMBtu ↔ kg

How this gas unit converter works

Gas is bought and sold in a confusing mix of units. Your meter counts cubic metres or cubic feet, your bill charges for kWh or therms, traders quote MMBtu, LNG ships carry tonnes, and propane is delivered by the litre or gallon. These units measure three different things (volume, energy and mass), so you can only convert between them if you know the properties of the gas.

Every conversion here goes through one quantity, gross energy in megajoules. Your input becomes MJ, and MJ becomes the target unit. Three properties of the selected gas make that possible:

• the gross calorific value (MJ per standard cubic metre) to link volume and energy;
• the gas density (kg per standard cubic metre) to link volume and mass;
• the liquid density (kg per litre) for LNG and LPG in liquid form.

Pick natural gas, LNG, propane, butane, biomethane or hydrogen and these fill in automatically. You can edit them in the advanced options to match your supplier’s specification. The energy basis switch shows energy units as gross (as on bills) or net (as in IEA and EU statistics). The full table lists your amount in all 18 units at once.

The formula

Worked example

The defaults convert 1,000 m³ of pipeline natural gas at 39.5 MJ/m³ gross:

• Energy = 1,000 × 39.5 = 39,500 MJ = 10,972 kWh (39.5 GJ)
• In therms: 10,972 ÷ 29.3071 = 374.4 therms, or 37.44 MMBtu
• In cubic feet: 1,000 ÷ 0.0283168 = 35,315 ft³ (35.3 Mcf)
• Mass at 0.757 kg/m³: 757 kg; liquefied as LNG at 0.45 kg/L that would occupy about 1,682 litres, roughly 600 times less space than the gas
• Burning it releases about 2,080 kg of CO₂

Switch the basis to net and the same gas shows about 9,900 kWh. Same molecules, different accounting convention.

How to read the results

• The headline tile shows your amount in the target unit.
• The tiles give the most-used equivalents: kWh, GJ, therms, MMBtu, standard volume, cubic feet, mass and liquid volume.
• The “in every unit” table also shows what one unit of your input equals, which is handy if you build your own spreadsheet.
• The reference table compares the gases per cubic metre and per kilogram. Note how propane holds about 2.4 times more energy per cubic metre than natural gas, while hydrogen holds less than a third. Per kilogram, though, hydrogen is by far the most energy-dense.

Typical values

Tips for accurate conversions

• Use the calorific value from your bill. It is measured continuously by the network operator and can differ from the default by a few percent.
• Check the reference conditions. Industrial contracts often use Nm³ (0 °C), domestic meters effectively report at around 15 °C. Mixing them up causes a 5.5% error.
• Know which basis your source uses. Comparing a net-basis boiler efficiency with a gross-basis gas price inflates apparent efficiency by about 10%. That is why condensing boilers can be quoted as “over 100% efficient” on a net basis.
• For bills, use the bill calculator. Domestic billing adds a volume correction factor; the gas cost calculator applies it for you.
• Comparing fuels? The heating cost comparison converts every fuel to cost per useful kWh.

Limitations

Conversions involving volume or mass depend on the gas composition, which varies by source and over time; the defaults are representative, not exact. Gas density and calorific value are treated as fixed at standard conditions, so the converter does not handle pressurised cylinders or real-gas compressibility at high pressure. LPG products are often propane–butane mixtures; for blends, enter intermediate values in the advanced options. CO₂ figures are stoichiometric combustion emissions only and exclude upstream methane leakage.

For billing disputes, always use the calorific value and correction factor printed on the bill itself, since suppliers publish daily or monthly averages for each network zone. For trading or LNG contracts, check whether prices are quoted per MMBtu on a gross basis (the US and Asian convention) or per MWh on a gross basis (European hubs such as TTF and NBP), and convert with the same basis on both sides.

Method & assumptions

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