Skip to main content

Free calculator

Use this calculator to

  • Price any block of kWh at your contract unit rate, in pence and pounds
  • Turn the difference between two meter readings into a cost figure
  • Check the energy line of an invoice before standing charge, CCL and VAT are added
  • Price the output of the energy consumption calculator without re-keying the maths

Energy Cost Calculator

Calculate electricity cost from energy (kWh) and your tariff rate.

kWh
p/kWh
Result
—

Formulas

  • Cost (pence) = kWh × rate (p/kWh)
  • Cost (£) = Cost (pence) / 100

Related Calculators

£/kWh

Electricity Bill

Estimate electricity cost from power usage and tariff rate

Open calculator
⚡kWh

Energy Consumption

Calculate total energy use over time for multiple appliances

Open calculator
kW→kWh

kW to kWh

Convert power (kW) and time to energy (kWh)

Open calculator

Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Supplier offers rarely line up cleanly on first inspection. One quote loads more onto the unit rate, another sits on a heavier standing charge, a third bakes in a non-commodity pass-through that only becomes visible months in once the first reconciliation lands. Reducing every offer to total £ at the consumption you actually use is the only honest comparison, and the standing-charge difference is the variable that most often hides the real ranking when the figures are read off the top of a quote.

On a 250,000 kWh per year site, a 2 p/kWh swing on the unit rate is £5,000 per year, and a £200 per year standing-charge gap is rounding error against it. On a 50,000 kWh per year SME, the same standing-charge gap is a quarter of the total spend differential, and the offer that looked cheapest on the unit rate may not be. The maths reverses around mid-market scale, which is where most decisions go wrong if they are made on headlines alone.

Purely Energy tenders to 30+ suppliers and presents every offer on the same total-£ basis at your actual consumption profile, with wholesale, non-commodity, supplier margin and our margin shown separately on the same page. Where the offer looks attractive but the structure is fragile (pass-through ratchets, end-of-term price step-ups, capacity assumptions that do not match your half-hourly profile), we flag it before the contract is signed, not after the bill arrives, so the offer that wins the tender is the offer that actually performs over the term.

Common questions

How do I calculate the cost of electricity from kWh?

Multiply the energy by your unit rate: cost in pence = kWh x rate (p/kWh), then divide by 100 for pounds. If a meter advanced 2,500 kWh over a month, the energy cost is 2,500 multiplied by your contracted pence per kWh. This is the variable part of the bill; the standing charge, the Climate Change Levy and VAT sit on top of it.

Where do I find my unit rate?

On your bill it appears as a pence per kWh line, and on a business contract it is in the price schedule. Half-hourly and two-register supplies carry several rates, typically day, night and sometimes evening and weekend bands. If your supply has more than one rate, split the kWh by band and run the calculation per rate, because applying a single blended figure understates or overstates the true cost.

Does the unit rate include the standing charge?

No. The unit rate prices each kWh consumed, while the standing charge is a separate fixed fee per day that covers metering and network connection regardless of usage. A low unit rate paired with a high standing charge can cost more overall for a low-consumption site than the reverse. When comparing contracts, multiply each quote's unit rate by your annual kWh and add 365 times its daily standing charge.

Why do businesses pay different unit rates for the same electricity?

Business rates are priced per contract, not from a public price cap. The rate reflects wholesale market levels on the day the contract was agreed, the contract length, your annual volume, your usage shape across the day, your region's distribution charges and your credit profile. Two neighbouring firms can hold very different rates simply because they signed in different market conditions, which is why retendering at the right time matters.

What is the difference between a fully fixed rate and a pass-through rate?

A fully fixed unit rate bundles the wholesale energy cost with non-commodity costs such as network charges and policy levies into one pence per kWh figure that holds for the contract term. A pass-through contract fixes only the energy element and recharges non-commodity costs at cost as they change. Fixed gives budget certainty; pass-through can track falling charges but exposes you to rises. Check which type your rate is before using it here.

Related calculators

The conversions that procurement and engineering use alongside this one.

Energy Cost Calculator | kWh to £ UK Tool | Purely Energy