The short version: a kilowatt-hour (kWh) is the energy used by a 1 kW appliance running for one hour. Your bill charges a unit rate — so many cent per kWh — multiplied by the kWh you used. kW measures how fast something uses energy; kWh measures how much it used.
The CRU’s typical Irish household uses 4,200 kWh of electricity and, where there is gas heating, 11,000 kWh of gas a year — about 11.5 and 30 kWh a day respectively.
What is a kilowatt-hour, exactly?
Start with the watt, the basic measure of electrical power. A thousand watts make a kilowatt (kW). Run something rated at one kilowatt for exactly one hour and it has used one kilowatt-hour (kWh) of energy. That is the whole definition: 1 kW × 1 hour = 1 kWh.
The two halves trade off against each other. A powerful appliance reaches 1 kWh quickly; a weak one takes ages. A 2 kW kettle gets there in 30 minutes of boiling. A 100 W television needs 10 hours. A 10 W LED bulb would have to burn for 100 hours — four days straight — to use the same energy the kettle used in half an hour. Same kWh, wildly different journeys.
Irish bills sometimes call a kWh a “unit” — the words mean the same thing. Your electricity meter is just a counter of these units: it ticks upwards forever, and each bill charges you for the difference between two readings. When a bill says 700 units at 38.04c, it is saying 700 kWh passed through the meter since the last reading, at a price per kWh.
What is the difference between kW and kWh?
This is the trap that catches almost everyone once, so let’s spring it gently. kW is power — a rate. kWh is energy — an amount. The cleanest analogy is driving: kW is your speed, kWh is the distance on the odometer. A car capable of 180 km/h that only ever does school runs covers very little distance; a 9 kW shower used for four minutes uses less energy than a 100 W fridge humming all day.
| kW (kilowatt) | kWh (kilowatt-hour) | |
|---|---|---|
| Measures | Power — how fast energy is being used right now | Energy — how much was used over time |
| Analogy | Speed (km/h) | Distance travelled (km) |
| Where you see it | Appliance labels, shower ratings, EV charger specs | Your bill, your meter, every unit rate |
| Example | A kettle rated 2 kW | That kettle boiling for 30 minutes = 1 kWh |
| What you pay for | Nothing — power is never billed directly at home | Everything — the usage line is kWh × unit rate |
The practical payoff: an appliance’s kW rating tells you how expensive it is per minute of use, not how expensive it is overall. The big-ticket items on an Irish bill are either high-power things used briefly but daily (showers, ovens, kettles) or low-power things that never switch off (fridges, routers). Both routes lead to the same place — kWh on the meter.
How many kWh does a typical Irish home use?
The CRU’s typical-usage figures — the ones every supplier must use when quoting an Estimated Annual Bill — are 4,200 kWh of electricity per year and 11,000 kWh of gas per year. Divided by 365, that is roughly 11.5 kWh of electricity a day and 30 kWh of gas a day on average.
Those two daily figures side by side — the gas number is bigger because heating a whole house takes far more raw energy than running its lights, screens and appliances:
Two caveats make these numbers more useful. First, they are averages of averages: a one-person apartment might use half the electricity figure, a family home with an EV double it — which is why our low-usage ranking prices plans at a stated 2,100 kWh instead. Second, the gas average hides a mountain range: usage piles into the heating months, so a winter day can burn several times that 30 kWh while a summer day burns almost nothing but hot water. Whether your own usage is high is a question with its own page.
Your real number beats any typical figure. Suppliers must print your annual consumption on the bill — find that kWh figure once and you can price any plan in the market against your actual life rather than the CRU’s statistical household.
How does cent per kWh become the euro amount on my bill?
The usage line on your bill is one multiplication: kWh used × unit rate = usage charge. Take a household tracking the CRU typical 4,200 kWh a year, billed every two months — about 700 kWh per bill. On Electric Ireland’s standard 24-hour rate of 38.04c per kWh (checked 28 August 2026), the arithmetic runs:
| Step | Arithmetic | Result |
|---|---|---|
| kWh this billing period | current reading − previous reading | 700 kWh |
| Usage charge | 700 kWh × 38.04c | €266.28 |
That is the engine of the bill, but not the whole bill. On top of the usage line sit the standing charge (a fixed daily fee you pay regardless of usage), the PSO levy on electricity, and 9% VAT on the lot. On NightSaver and smart plans the single multiplication becomes two or three — one per time band, each with its own rate. The full anatomy, line by line, is in electricity bill explained.
The unit rate is also where plans genuinely differ, which makes it the number to compare when switching. The standard rates we verified on 28 August 2026 ranged from Electric Ireland’s 38.04c to Energia’s 42.65c — on 4,200 kWh, that spread alone is 4,200 × 4.61c ≈ €194 a year, before any new-customer discount enters the picture. Our cheapest electricity ranking does this arithmetic across the market, for year 1 and year 2.
Why is my gas bill in kWh when the meter counts cubic metres?
Your gas meter measures volume — cubic metres of gas through the pipe — but you are buying heat, and the energy in a cubic metre varies slightly with the gas mix and pressure. So Gas Networks Ireland converts the metered volume into kWh using a conversion factor and a calorific value printed on the bill, and your supplier prices those kWh exactly as an electricity supplier would: unit rate × kWh, plus standing charge, carbon tax and VAT. One useful consequence of both fuels sharing a unit: you can compare them per kWh, and gas is roughly a third of the price — on the Electric Ireland rates above, 38.04c for an electricity kWh against a discounted 11.016c for gas. The conversion sums, worked in full, are in gas bill explained.
What do everyday appliances actually cost per use?
Every figure below is our own arithmetic, not a measurement: kW rating × minutes ÷ 60 = kWh, then priced at Electric Ireland’s standard 24-hour rate of 38.04c per kWh including VAT, checked 28 August 2026. Your appliance’s wattage is on its rating plate or manual, and your unit rate is on your bill — swap in your own numbers and the same formula prices anything in the house.
| Appliance | Rating | Running time | The formula | Cost at 38.04c/kWh |
|---|---|---|---|---|
| LED bulb | 0.01 kW (10 W) | 5 hours (300 min) | 0.01 × 300 ÷ 60 = 0.05 kWh | 1.9c |
| Kettle | 2 kW | 3 min | 2 × 3 ÷ 60 = 0.1 kWh | 3.8c |
| Wi-Fi router | 0.01 kW (10 W) | 24 hours (1,440 min) | 0.01 × 1,440 ÷ 60 = 0.24 kWh | 9.1c |
| Electric shower | 9 kW | 10 min | 9 × 10 ÷ 60 = 1.5 kWh | 57.1c |
| Oven | 2.5 kW | 1 hour (60 min) | 2.5 × 60 ÷ 60 = 2.5 kWh | 95.1c |
| Portable heater | 2 kW | 3 hours (180 min) | 2 × 180 ÷ 60 = 6 kWh | €2.28 |
The table teaches the two lessons that matter. Lesson one: power × time is everything. The kettle’s scary 2 kW costs less than 4c per boil because three minutes is nothing; the shower at 9 kW is the dearest ten minutes in the house; and the modest 2 kW heater becomes the most expensive line of all simply because it runs for hours. Lesson two: the always-on trickle adds up — a 10 W router is invisible per day at 9c, but that is a 0.24 kWh × 365 = 87.6 kWh a year, about €33 at this rate, for one small box.
This is deliberately not a fifty-row wattage encyclopaedia — the formula is the point, not the catalogue. If working through your own big-ticket items leaves you wanting to shrink them, the practical moves (and which ones are worth the bother) are in how to reduce your electricity bill.
What should I do with this number?
Three things, in rising order of savings. Read your annual kWh off the bill — it turns every plan in the market into a comparable euro figure. Compare unit rates on your usage, not on discount percentages: a big % off a dear standard rate can lose to a small % off a cheap one, and the year-2 cliff is priced in kWh too. And when you are ready, switching takes one form and 2–4 weeks — the walkthrough is in how to switch, and the market view is on best energy in Ireland. One honesty note: matched.ie is not a CRU-accredited price-comparison site — the accredited comparators are listed on cru.ie if you want a regulated tool.
