How to work out your energy usage and calculate kWh costs

If your energy bills have jumped and you’re thinking “surely we’re not using that much…”, you’re not alone.

The good news: working out your electricity usage in kWh is genuinely simple once you know the difference between kW and kWh (the bit that trips almost everyone up). And once you’ve got your “daily kWh”, you can benchmark it against UK averages and spot the easiest ways to cut it.

The basics: understanding kW vs kWh

Let’s make this painless as this can be a little confusing. 

• kW (kilowatts) = power (how fast electricity is being used)
• kWh (kilowatt-hours) = energy (how much electricity you used over time — what you’re billed for)

A simple analogy:

• kW is like speed (miles per hour)
• kWh is like distance travelled (miles)

So, you buy electricity in kWh, but appliances are usually rated in W or kW.

Is 200W the same as 200Wh?

The short answer is, No.

• 200W tells you the rate the appliance uses electricity (power).
• 200Wh tells you the amount of energy used over time.

Example:

• A 200W device used for 1 hour uses 200Wh (which is 0.2kWh).

Ofgem puts it neatly: 1 kWh is enough to run a 100W light bulb for 10 hours. (ofgem.gov.uk)

How to calculate your energy usage (the formula)

Here’s the simple formula:

(Device wattage × hours used) ÷ 1000 = kWh

Worked example: TV

Say your TV is 200W and you watch it for 5 hours:

• 200 × 5 = 1,000Wh
• 1,000 ÷ 1,000 = 1 kWh

So that TV session used 1 kWh.

Converting kWh into cost (roughly)

To estimate cost:

kWh used × your unit rate = cost

If you’re on a standard variable tariff paying by Direct Debit, Ofgem’s price cap unit rate for electricity (1 April–30 June 2026) is 24.67p per kWh on average (rates vary by region and payment method). (ofgem.gov.uk)

So that 1 kWh TV session costs about £0.25 (25p-ish).

If your totals feel high, that’s where options like installing solar panels (generating your own renewable electricity) can start offsetting a big chunk of the daytime usage.

Benchmarking: what is a “normal” energy usage in the UK?

Ofgem’s Typical Domestic Consumption Values (TDCVs) are a helpful benchmark for low/medium/high usage households: (ofgem.gov.uk)

• Low: 1,800 kWh electricity/year (flat or 1-bed; 1–2 people)
• Medium: 2,700 kWh electricity/year (2–3 bed; 2–3 people)
• High: 4,100 kWh electricity/year (4+ bed; 4–5 people)

To convert daily to yearly, multiply by 365.

Is 12 kWh per day a lot?

12 kWh/day × 365 = 4,380 kWh/year.

That’s above Ofgem’s “high” benchmark (4,100 kWh/year) for a typical household. (ofgem.gov.uk)

But: it can be totally understandable if you have things like:

• an EV charging at home
• a heat pump
• a lot of home working
• electric showers / electric cooking / a big household

Is 7000 kWh per year a lot?

Yes — 7,000 kWh/year is very high for typical domestic electricity usage (well beyond Ofgem’s “high” benchmark). (ofgem.gov.uk)

Why households differ so much

Your kWh will swing based on:

• home size and insulation
• number of people
• whether heating/hot water is gas or electric
• lifestyle (WFH, gaming PCs, tumble drying, etc.)

Which appliances use the most electricity?

Big hitters are usually anything that heats (water, air, food) or runs for ages:

• Electric showers
• Immersion heaters
• Tumble dryers
• Ovens / hobs
• Dishwashers / washing machines (especially hot washes)

Energy Saving Trust notes that washing machines, dishwashers and tumble dryers are among the biggest regular appliance contributors to bills, largely because of the energy needed to heat water or air. (energysavingtrust.org.uk)

Ofgem also gives some “typical appliance” examples (these vary by model and use):

• fridge-freezer: ~1 kWh in 26 hours
• electric oven: ~2 kWh for 30 minutes
• tumble dryer: ~4.5 kWh per cycle

(ofgem.gov.uk)

How much does it cost to run a washing machine for 2 hours?

A common rough rating for a washing machine while heating is around 2kW (2,000W).

Calculation:

• 2kW × 2 hours = 4 kWh
• 4 kWh × 24.67p ≈ 98.7p (about £1.00) using the price cap unit rate as a guide

Real-world note: washing machines don’t draw maximum power constantly — the heating phase uses the most, then it drops.

Will 200W run a refrigerator?

Kind of, but here’s the catch:

• A fridge-freezer is usually low average power across the day because it cycles on and off.
• But it needs a higher start-up surge when the compressor kicks in.

That’s why power stations/inverters need to handle surge watts, not just the average number.

Solar sizing: will a solar panel run my house?

This is where people often mix up system size (kW) with daily energy (kWh).

Is 10kW enough to run a house?

A 10kW solar PV system is very large for many UK homes, but the more important point is:

• Your home can draw 10kW instantly if multiple high-load appliances run together (shower + oven + kettle = chaos).
• Solar output varies with daylight and weather, so solar alone won’t match peaks unless you have a system designed for it and (usually) battery storage.

Solar helps most with your baseload (always-on stuff like fridge, broadband, standby loads) plus daytime usage. Batteries help shift that solar energy into the evening.

“How long does it take for a 200W solar panel to charge a 100Ah battery?”

You can do a rough estimate like this:

1) Convert battery capacity to watt-hours:
Battery Wh = Ah × Voltage

Example assumptions (because this varies):

• 100Ah battery at 12V → 100 × 12 = 1,200Wh (or 1.2kWh)

2) Divide by solar power (then allow for losses):

• Best-case: 1,200Wh ÷ 200W = 6 hours of full output
• More realistic: allow for losses + non-perfect sun (say 60–80% effective). That could make it more like 7–10+ hours of decent sun.

If you’re looking to store energy for later, a home battery storage system is designed to do this safely and efficiently (and in a way that suits UK households and tariffs).

How to reduce your daily kWh usage

Quick wins (you can do this week)

• Standby/vampire devices: TVs, soundbars, consoles, chargers, set-top boxes can nibble away 24/7.
• LED lighting: If you’ve still got older bulbs, LED upgrades are an easy win.
• Washing habits: lower temperatures and full loads (often where the real savings are).
• Drying: tumble dryers are convenient… and hungry. Air-dry when you can.

Does turning off lights save kWh?

Yes — technically. But it depends on the bulb:

• Old bulbs: noticeable.
• LEDs: still worth it, but the saving is smaller because LEDs use much less energy per hour.

Long-term (the big lever)

If you’ve already trimmed the obvious waste and you’re still consistently high, the long-term move is generating your own electricity to cover as much of your baseload and daytime usage as possible, and using a battery to shift spare solar into the evening.

Frequently asked questions

Is 40 kWh per day a lot in the UK?

Yes — for most standard homes, 40 kWh/day is extremely high. It usually points to something major (EV charging, heat pump, electric heating/immersion, or significant wastage). Compare it against Ofgem’s benchmarks: even “high” electricity usage is 4,100 kWh/year, which averages about 11.2 kWh/day. (ofgem.gov.uk)

How do I convert W to kWh?

1) Divide watts by 1,000 to get kW
2) Multiply by hours used to get kWh

Example: 500W heater for 3 hours

• 500W = 0.5kW
• 0.5 × 3 = 1.5 kWh

How many kW does a normal house use daily?

Most people mean kWh (energy), not kW (power).

Using Ofgem’s “medium” electricity benchmark (2,700 kWh/year):
2,700 ÷ 365 ≈ 7.4 kWh/day (ofgem.gov.uk)

Conclusion and next steps

Knowing your daily kWh usage is the first step to getting control of your bills. Once you’ve calculated it, you can:

1. benchmark against UK averages,
2. spot the biggest appliance culprits,
3. decide whether quick fixes will do the job — or whether you need a bigger solution.

If your daily electricity usage is consistently over 10 kWh, a solar and battery system could significantly reduce your grid reliance (especially for daytime usage and baseload). If you want a tailored recommendation, request a bespoke system design and we’ll help you size it properly.