The short version: an Irish gas bill is unit rate × kWh used, plus a standing charge for the days in the period, plus carbon tax at about 1.25c per kWh including VAT, with 9% VAT on the lot. There is no PSO levy on gas — that lives on electricity bills only. Your meter counts cubic metres; the bill converts them to kWh using two factors printed beside the reading.
This is the gas half of a pair — the electricity half is at electricity bill explained. And the usual honesty note: matched.ie is not a CRU-accredited price-comparison site; the accredited comparators are listed on cru.ie.
What are the lines on an Irish gas bill?
Every supplier lays the page out differently — Bord Gáis Energy and Flogas bills do not look alike — but the same lines appear on all of them, because the CRU requires them to. Here is the anatomy, top to bottom, with what each line actually means:
| Bill line | What it is | What to check |
|---|---|---|
| GPRN | 7-digit number identifying the gas connection at your address. Belongs to the property, not to you or your supplier. | You need it to switch supplier. It never changes. |
| Meter readings | Opening and closing reads in units (cubic metres on a metric meter), with a letter beside each: A for actual, E for estimated. | An E means the bill is a guess — see below. |
| Conversion to kWh | Units × correction factor × calorific value ÷ 3.6. Both factors are printed here. | The sum is checkable — see the conversion section. |
| Unit rate × kWh | The converted kWh multiplied by your tariff’s cent-per-kWh rate. The biggest line in winter by far. | Is the rate still your discounted rate, or has the year-2 snap-back happened? |
| Standing charge | A fixed daily amount for the days in the billing period, owed even at zero usage. | One national rate per tariff — no urban/rural split, unlike electricity. |
| Carbon tax | Government excise on natural gas: about 1.25c per kWh including VAT at today’s rate. | Same on every supplier — switching cannot reduce it. |
| Discount | Your new-customer percentage off, usually applied to the unit-rate line only. | Note what it applies to — rarely the standing charge or carbon tax. |
| VAT at 9% | Applied to everything above: units, standing charge and carbon tax. | The 9% rate runs to 31 December 2030. |
| No PSO levy | Deliberately absent — the PSO is an electricity-only charge. | If you are looking for it, it is on your electricity bill. |
Somewhere on the page you will also find your tariff name, your contract end date (worth diarising — it is when the discount dies), your annual consumption figure, and the billing period. That annual kWh number is the single most useful figure on the bill: it is what lets you compare tariffs on your usage rather than the CRU’s typical 11,000 kWh.
How do the unit rate and standing charge work on gas?
The unit rate is the price of energy itself: a fixed number of cent for every kilowatt-hour of gas you burn. Unlike electricity, where NightSaver and smart tariffs slice the day into price bands, gas has one flat rate around the clock — a kWh at 3am costs the same as a kWh at 6pm. There is no gas equivalent of a time-of-use plan, which makes gas tariffs easy to compare: rate, standing charge, done. If you want the deeper primer on what a kilowatt-hour actually is, that is its own page.
The standing charge is the fixed cost of being connected: it accrues per day, covers the pipes, the meter and the meter-reading service, and is owed in full even in a month where you burn nothing — which, for gas, describes most Irish summers. That makes the standing charge proportionally brutal on low-usage gas homes: on a July bill it can be the biggest line on the page. One structural difference from electricity is worth knowing: gas standing charges have no urban/rural split. Electricity bills charge rural (DG2) homes a higher standing charge than urban (DG1) ones; a gas tariff has a single standing charge wherever the pipe runs. The full mechanics — and which suppliers load the standing charge versus the unit rate — are on the standing charges guide.
The discount line is where the marketing lives. A “30% off” gas deal is almost always 30% off the unit rate only — the standing charge and carbon tax usually ride along at full price. That is why two tariffs with the same headline percentage can produce different bills, and why our cheapest gas ranking compares full-year estimated bills rather than percentages.
How much carbon tax and VAT is on a gas bill?
Carbon tax is the line that makes a gas bill structurally different from an electricity bill. Electricity has the PSO levy and no carbon tax line; gas has carbon tax and no PSO. You never pay both on one fuel.
The Natural Gas Carbon Tax is set by Revenue, and the current rate — in force since 1 May 2025 — is €11.48 per MWh, which is 1.148c per kWh before VAT, or about 1.25c per kWh once the 9% VAT is added. At the CRU’s typical gas usage of 11,000 kWh a year, that works out at roughly €138 a year including VAT. It is identical on every supplier and every tariff: switching changes your unit rate and standing charge, never the carbon tax.
Dated and diarised: the carbon tax basis rises from €63.50 to €71 per tonne of CO2 on 14 October 2026 — an increase originally pencilled for May 2026 and postponed. Scaling Revenue’s per-MWh rate to the new basis puts the charge at roughly 1.28c per kWh before VAT — around 1.4c including VAT — which adds in the region of €15 a year at typical usage. Every supplier will pass it through on the same date; none of them chose it.
VAT on residential gas is 9%, the same reduced rate as electricity, and Budget 2026 extended it to 31 December 2030. It applies to the entire bill — units, standing charge and carbon tax — and appears as its own line just above the total. The wider story of the tax, including why electricity escapes it, is on the carbon tax guide.
How do cubic metres on the meter become kWh on the bill?
Your gas meter does not measure energy. It measures volume — cubic metres on a modern metric meter, hundreds of cubic feet on the older imperial ones — because volume is what physically flows through it. But suppliers must bill in kilowatt-hours, so every bill runs the reading through a conversion that Gas Networks Ireland calculates and the CRU has approved. The mechanism:
| Step | Factor | Where it comes from |
|---|---|---|
| 1. Units used | Closing read − opening read | Your meter. On an imperial meter the units are first multiplied by 2.83 to become cubic metres. |
| 2. × correction factor | Printed on your bill | Adjusts the measured volume to standard temperature and pressure — gas expands and contracts, so a “cubic metre” at your meter is standardised before pricing. A little over 1 on domestic bills. |
| 3. × calorific value | Printed on your bill (MJ/m³) | The energy content of the gas, measured continuously by Gas Networks Ireland — it varies with the gas in the pipe. GNI’s permitted range is 36.9–42.3 MJ/m³. |
| 4. ÷ 3.6 | Fixed | Pure unit conversion: 3.6 megajoules is exactly one kilowatt-hour. |
So the sum on every metric bill is:
kWh = units used × correction factor × calorific value ÷ 3.6
Worked with round numbers, purely as an illustration: 100 m³ × a correction factor just over 1 × a calorific value of 39 MJ/m³ ÷ 3.6 ≈ 1,090 kWh — take the two real factors from your own bill, because the calorific value changes with the gas actually in the network. The lazy sanity check: one metric unit is roughly 11 kWh. If a bill claims you used 200 units and charges you for 5,000 kWh, something is wrong.
Two practical notes. First, the calorific value is not a supplier choice — Gas Networks Ireland measures it across the network and supplies the figure, so two suppliers billing the same period at the same address use the same conversion. Second, this is why you should always compare gas tariffs in cent per kWh, never “per unit”: the kWh is the standardised product. How to physically read the dials and digits is covered in how to read a gas meter.
What is the GPRN and why does it matter?
Near the top of the bill sits the GPRN — Gas Point Registration Number — a 7-digit number that identifies the gas connection at your address on Gas Networks Ireland’s register. It is the gas twin of the electricity MPRN (which is 11 digits and starts with 10), and the same rules apply: it belongs to the property, not to you, not to your meter and not to your supplier, so it survives every switch and every change of tenant.
You will be asked for it exactly twice in normal life: when you switch supplier, and when you move into a home and register the gas account in your name. If you cannot find it — no bill, new build, previous occupant took the paperwork — find your GPRN walks through the options, and who is my supplier covers the related mystery of moving in with no idea who bills the address.
What does an estimated read mean on a gas bill?
Beside each meter reading is a letter: A for actual — someone read the meter, or you submitted the figure — and E for estimated. Gas is more estimate-prone than electricity for a structural reason: the national smart-meter rollout is an electricity programme, so while a smart electricity meter reports itself remotely, virtually every domestic gas meter in Ireland is still read in person by Gas Networks Ireland’s meter readers, who call only a few times a year. Every bill in between is built on an estimate of what a home like yours probably used since the last real read.
Estimates are not malicious, but they are dangerous in both directions — and worst on gas because usage is so seasonal. An estimate rolled forward from a mild autumn can undercharge you all winter and then land the true cost in one grim catch-up bill when a real read finally happens. The fix costs two minutes: photograph the meter and submit the reading through your supplier’s app or website just before the bill is due. The next bill is then anchored to reality, and any drift from earlier estimates unwinds automatically. The full pattern — spotting a bad estimate, disputing a silly one — is on estimated readings explained.
Why is my winter gas bill so much bigger than summer?
Because for most Irish homes, gas is heating. Electricity use bumps up modestly in winter — more lighting, more kettle — but gas use transforms: the same house that idles along on hot water and a hob all summer suddenly runs a boiler for hours a day. The result is that a gas year is not twelve similar months; it is four heavy months, four light ones, and four in between. Shaped roughly, the winter weighting looks like this — illustrative shares of a year’s gas use, not euro and not measured data:
Read those bars and two things fall out. First, December to February can carry more gas than May to October combined — so a shocking January bill usually reflects the season, not a price change, and a lovely July bill proves nothing about your tariff. Second, the 11,000 kWh Estimated Annual Bill figure that suppliers quote is an annual total at the CRU’s typical usage — it is not a monthly figure twelve times, and no single bill should match one-sixth of it.
The neighbour trap: comparing your summer gas bill to a neighbour’s quoted annual EAB — or multiplying a summer bill by six — will convince you that one of you is being robbed, and it will be wrong. A €40 August bill and an €1,100 annual EAB can describe the same house on the same tariff. The only fair comparisons are annual kWh against annual kWh (both printed on your bills), or the same billing period year on year. What a normal annual figure looks like is on average gas bill in Ireland.
If the winter swing wrecks your budgeting, most suppliers offer a level-pay or budget plan that averages the year into equal monthly payments — you are not paying less, just flattening the shape. And if the bills themselves are the problem rather than the shape of them, the levers are the usual ones: check whether your discount has lapsed onto the standard rate, and price the alternatives on the cheapest gas ranking — or dual fuel if your electricity is up for a move too, with the unbundling maths in the dual fuel guide.
Where to next?
- Electricity bill explained — the sister page: PSO, urban/rural standing charges, MCC codes and day/night registers.
- Cheapest gas in Ireland — gas-only tariffs ranked on year-1 and year-2 cost at 11,000 kWh.
- Average gas bill in Ireland — what a normal year costs, and where your usage sits.
- Gas vs electric heating — whether the boiler still wins on running cost.
- How to switch energy supplier — GPRN in hand, the move takes one form and 2–4 weeks.
- Best energy in Ireland — the full supplier ranking, if the bill has talked you into leaving.
Primary sources for the figures on this page: Revenue’s Natural Gas Carbon Tax rates at revenue.ie, Gas Networks Ireland’s billing and calorific-value publications at gasnetworks.ie, and the CRU’s consumer pages at cru.ie.
