What Is a kWh? The One Idea That Makes Your Energy Bill Make Sense

What is a kWh?

A kWh (kilowatt-hour) is one unit of energy. It is the amount of energy a 1,000-watt device uses if you leave it running for one hour. That is it. When your supplier bills you, they count how many of these units you used and charge you per kWh.

A "kilowatt" (kW) is just 1,000 watts. So a 1,000 W heater is a 1 kW heater. Run it for one hour and it uses 1 kWh. Run a 2 kW heater for one hour and it uses 2 kWh. Run that same 2 kW heater for half an hour and it uses 1 kWh. The sum is simple: kWh = power in kW × hours.

Why does this matter? Because everything on your bill is in kWh. Your gas, your electricity, the price cap, the cheapest deals on a comparison site, all of it is priced per kWh. Once you can picture one kWh, the whole bill stops being a wall of jargon.

kW vs kWh: the speed-vs-distance trick

This is the bit most people get muddled, and it is the bit worth nailing. A kW and a kWh sound almost the same, but they measure two different things:

• ✓A kW is how fast you use energy, like the speed on a car's speedometer. A 3 kW kettle is "faster" than a 100 W lamp;
• ✓A kWh is how much you have used, like the miles you have travelled. It is speed multiplied by the time you kept going.

Your bill is in kWh, the distance, never in kW, the speed. That single fact explains something that surprises a lot of people: a powerful 3,000 W kettle used for 3 minutes costs less than a weedy 100 W device left on all day. The kettle is fast but brief. The little device is slow but never stops. Distance, not speed, is what you pay for.

Quick check: the 3,000 W kettle for 3 minutes uses about 0.15 kWh. The 100 W device left on for 24 hours uses 2.4 kWh, sixteen times more. The "powerful" appliance is the cheap one here, purely because of how long each one runs.

Why most "what is a kWh" explanations get it wrong

Search this question and you will hit the same two mistakes again and again. They are worth spotting, because each one leaves you more confused than before:

• ✓They mix up kW and kWh as if they were the same word. They are not: one is a rate, the other is a total. Treating them as interchangeable is like confusing miles per hour with miles;
• ✓They give you one rate for both fuels, as if a kWh always costs the same. It does not. A kWh of gas and a kWh of electricity are the same amount of energy but very different prices, and missing that is why so many people are baffled by their heating bill.

So we will keep the two ideas separate. First, use the converter below to feel how power and time turn into kWh and cost. Then we will look at why the same unit costs so differently depending on the fuel.

What is a kWh of electricity?

A kWh of electricity is one unit of electrical energy: enough to run a 1,000 W appliance for an hour. In 2026 it costs 24.67p on the Ofgem price cap. That single unit does a surprising amount of work. It will boil roughly 10 cups of tea in a kettle, run a 50-inch TV for about 5 hours, or keep a 1,000 W fan heater going for one hour.

Electricity is the most flexible energy in your home: it runs lights, screens, chargers, the fridge and the washing machine. The catch is the price. Of the two fuels most UK homes use, electricity is by far the dearer one per kWh.

What is a kWh of gas?

A kWh of gas is the exact same amount of energy as a kWh of electricity. The energy is identical: one unit is one unit. What is different is the price and the job. In 2026 a kWh of gas costs just 5.74p on the price cap, roughly a quarter of the electricity price.

Most homes use gas for the big, heat-hungry jobs: the boiler for hot water and central heating, sometimes the hob. Because heating burns a lot of kWh, doing it with the cheaper fuel is why a gas-heated home usually pays less for warmth than an all-electric one. The energy is the same; the bill is not.

What is the cost of a kWh in the UK?

On the Ofgem price cap for 1 April to 30 June 2026 (Direct Debit), a kWh of electricity costs 24.67p and a kWh of gas costs 5.74p. Those are capped rates: your supplier cannot charge more than this per unit, though a fixed deal might charge a little less.

The price you actually pay can sit a touch above or below these figures depending on your region, your tariff and how you pay (Direct Debit is the cheapest method). But the cap is the number to anchor on, and the headline takeaway never changes: electricity is about four times the price of gas for the same kWh.

Numbers are easier to trust when you can picture them. Here is what 1 kWh actually does, what a single kWh of electricity buys you in real life:

Figures are typical everyday approximations. Real appliances vary by model; check the rating plate for the exact wattage.

The 4× truth that explains your heating bill

Here is the fact that ties the whole page together. One kWh is one kWh: the same packet of energy. Yet that identical unit costs about four times more as electricity (24.67p) than as gas (5.74p). This is not a rounding quirk. It is the single most useful thing to know about UK energy.

It is why electric heating has a reputation for being expensive. A plug-in electric heater turns each kWh into one kWh of heat, but at the dear electricity price. A gas boiler delivers its heat from the cheap fuel instead. Same warmth, very different cost.

So how can electric heating ever compete? With a heat pump. A heat pump does not burn the electricity to make heat: it uses it to move heat from the outside air into your home. For every 1 kWh of electricity it draws, it delivers about 3 kWh of heat. That 3-for-1 trick is the only way the expensive fuel beats the cheap one, because it cancels out most of the 4× price gap.

The one fact to remember A kWh of electricity costs about 4× a kWh of gas. That gap explains nearly everything: why gas heats homes cheaply, why electric heaters feel expensive, and why a heat pump (3 kWh of heat per 1 kWh of electricity) is the only electric heating that competes with a gas boiler.

How to read your bill in kWh

Your bill is built from your kWh, so reading it is mostly about finding that number. Here is how to make sense of it:

• ✓Find your kWh used. Your bill or smart meter app shows the units used for the period, one figure for electricity and one for gas. That is your "distance" travelled;
• ✓Find your unit rate. It is the pence-per-kWh price, listed separately for each fuel. Multiply your kWh by the rate to get the energy part of your bill;
• ✓Add the standing charge. This is a daily fee you pay even at zero kWh. It is on top of the per-kWh cost, not part of it;
• ✓Compare your electricity and gas kWh. If most of your kWh are electricity and your bill is high, the 4× price gap is likely the cause, and the heating type is worth a look.

The bottom line

A kWh is one unit of energy: what a 1,000 W device uses in an hour. The trick that makes it stick is speed versus distance: a kW is how fast you use energy, a kWh is how much you have used, and your bill only ever charges you for the distance. That is why a brief blast of a powerful kettle is cheap and a slow trickle of a device left on all day is not.

And the one number to carry away: the same kWh costs about four times more as electricity than as gas. Know your kWh, know which fuel they are, and you know exactly where your bill is coming from, and where the savings hide.