Gas Is Bought in Gigajoules and Specified in Megajoules per Cubic Metre
A pipeline contract prices energy per gigajoule. The gas quality clause immediately below it is written in megajoules per cubic metre, and so is the daily figure the metering station telemeters back. Anyone confirming a nomination, checking an allocation statement or valuing a cargo spends the day stepping between the two, because the quantity that gets invoiced is volume multiplied by calorific value — and that product lands in megajoules before anyone rounds it into gigajoules.
Why the Contract Refuses to Talk in Volume
Volume Alone Does Not Say What Was Delivered
Standard Conditions Are Part of the Number
A Cargo Is Energy, Not Cubic Metres
Working a Nomination From Flow and Calorific Value to Gigajoules
The arithmetic is simple; the discipline is in keeping the units and the reference conditions straight at every step.
Multiply volume by the gas quality figure
Take the metered standard cubic metres for the period and multiply by the calorific value from the same station's chromatograph. The product is in megajoules, which is where most quality-and-quantity working papers naturally sit.
Convert that product to the contract unit
Enter the megajoules and the gigajoule figure appears beside it. Cargo-scale numbers stay legible because the thousands are spaced out, and only past ten billion does the display move to exponent form.
Price the quantity in the market's own unit
A gigajoule is 0.947813 MMBtu and 0.277778 MWh, so $10/MMBtu is $9.48/GJ and €30/MWh is €8.33/GJ. Convert the quantity first and the price second; doing both at once is where errors hide.
Reverse it to audit an allocation statement
Given a confirmed quantity in GJ, the swap arrows return the megajoules, which divided by the day's calorific value gives back the volume the meter should have registered. That round trip catches transposed quality figures quickly.
Contract and Cargo Quantities From Flow Rate to Gigajoules
Each row multiplies a volume or flow by a stated calorific value and shows where it lands. The LNG row uses 21 500 MJ per cubic metre of liquid, which is the conventional order of magnitude once the roughly 600-fold expansion to gas is taken into account.
| Quantity | Volume or flow | Calorific value | Energy (MJ) | Contract quantity (GJ) |
|---|---|---|---|---|
| One cubic metre | 1 m³ | 38.0 MJ/m³ | 38 | 0.038 |
| Small industrial site, one day | 1,000 m³/h × 24 h | 38.5 MJ/m³ | 924,000 | 924 |
| Daily nomination | 100,000 m³ | 37.5 MJ/m³ | 3,750,000 | 3,750 |
| One million standard cubic feet | 28,317 m³ | 39.0 MJ/m³ | 1,104,363 | 1,104.36 |
| Monthly contract volume | 3,000,000 m³ | 38.0 MJ/m³ | 114,000,000 | 114,000 |
| Standard LNG cargo | 160,000 m³ of liquid | 21,500 MJ/m³ | 3,440,000,000 | 3,440,000 |
The last two rows explain why traders keep several units in their head at once: 114,000 GJ of monthly pipeline gas is 108,000 MMBtu, while the cargo's 3.44 million GJ is about 3.26 million MMBtu or 956 GWh — the same energy quoted three ways depending on whether the counterparty prices off the Japan/Korea marker, off TTF, or off a domestic gigajoule contract.
What Earns Its Place on the Gas Desk
Nomination Sizes Recomputed as the Quality Moves
Because the result follows each keystroke, running the same volume against 37.0, 38.5 and 40.0 MJ/m³ takes seconds and shows immediately how much of a settlement difference gas quality is worth.
Plain GJ Digits for the Trade Confirmation
The copy control returns the figure without the unit or the thousands spacing, which is what a confirmation template or a position sheet needs if the total at the bottom is going to add up.
Take a Contract GJ Figure Back to Megajoules
Reversing the direction is how you check a metering report against a confirmed quantity, since dividing the recovered megajoules by the day's calorific value should reproduce the volume on the station log.
therm, BTU and MWh for Cross-Market Checks
One MMBtu is ten therms, and TTF trades per MWh. Both dropdowns search all 23 energy units, so a gigajoule quantity can be laid against the units another marker quotes without leaving the page.
Questions From the Gas Desk About Energy-Based Quantities
How does a gas quality figure in MJ/m³ become a contract quantity in GJ?
Multiply the standard cubic metres delivered by the calorific value measured over the same period, which gives megajoules, then divide by a thousand. A day of 100,000 m³ at 37.5 MJ/m³ is 3,750,000 MJ and therefore 3,750 GJ. In practice the calorific value is not a single number: chromatographs sample continuously, and the contract specifies whether settlement uses a flow-weighted average for the day, the month, or a zone value published by the transmission operator. Two parties multiplying the same volume by differently averaged quality figures will not reconcile, and the gap grows with how much the composition swings.
Why is pipeline gas sold by energy rather than by volume?
Because a cubic metre is not a consistent product. Methane-rich lean gas, gas with a heavy ethane and propane fraction, and gas diluted with nitrogen or carbon dioxide all occupy the same space while delivering measurably different heat. Buyers need heat, so energy-based custody transfer removes the argument: the seller is paid for what the gas can do rather than for how much of it there is. It also makes blending, storage cycling and cross-border flows accountable, since gigajoules in and gigajoules out can be balanced even when the composition changes along the way.
What does the Wobbe index add beyond calorific value?
Interchangeability. Wobbe is the gross calorific value divided by the square root of the gas's relative density, so gas at 38 MJ/m³ with a relative density of 0.60 has a Wobbe index of about 49.1 MJ/m³. Two gases with the same Wobbe deliver the same heat through the same burner orifice at the same pressure, even if their calorific values differ — which is exactly what a network operator cares about when appliances downstream cannot be re-jetted. That is why entry specifications set a Wobbe band, commonly somewhere in the 47–54 MJ/m³ range, alongside the calorific value limits, and why a rich imported cargo may need nitrogen ballasting before it can enter a lean network.
How does a price per gigajoule compare with one per MMBtu or per MWh?
One MMBtu is 1,055.06 MJ, so a gigajoule is 0.947813 MMBtu and a price of $10/MMBtu equals $9.48/GJ. One MWh is 3,600 MJ, so a gigajoule is 0.277778 MWh and €30/MWh works out at €8.33/GJ. Those three ratios are all a desk needs to move between the Japan/Korea marker, TTF and a domestic gigajoule contract, but currency and delivery point usually matter more than the arithmetic: a JKM cargo price is delivered ex-ship in Asia, while a hub quote is at the hub, and the freight and regasification between them can exceed the unit conversion several times over.
Why does the energy in an LNG cargo change from one loading to the next?
Composition and volume both move. LNG from different liquefaction trains carries different fractions of ethane, propane and nitrogen, which shifts the energy per cubic metre of liquid by several per cent, and the loaded volume itself varies with tank gauging, temperature and how much heel was retained. Boil-off during the voyage removes mostly methane, so the delivered gas is slightly richer than the loaded gas. This is why a cargo is measured at both ends: gauge tables and a composition analysis produce a certified energy quantity in GJ or MMBtu, and it is that figure, not the nameplate 160,000 m³, that the invoice is written against.
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