Small loads matter when repeated across many devices for many hours, but measuring is better than assuming.
The result is not a supplier bill or quote. Unit rates, standing charges, region, payment method, meter type, tariff, VAT, discounts, debt and support schemes can differ. Use values from the same tariff period and bill for a personal check.
Calculate standby use
Use a suitable plug meter for very low power.
The calculation runs in your browser. Values are not sent to the website.
How the calculation works
kWh = watts × hours × days ÷ 1,000 × number of devices.
Unit-rate energy and daily standing charges are shown separately wherever possible. That prevents a misleading single pence-per-kWh figure.
Worked example in pounds
Six devices at 2.5 W for 20 hours daily use about 109.5 kWh a year.
The example checks the method. It is not a universal tariff or a forecast of your next bill.
What changes the result
The largest differences usually come from:
- network standby
- quick start
- device count
- hours
- meter accuracy
How to improve the estimate
Use rates for your region, payment method and meter, including VAT consistently. Match the number of days and do not add standing charges or discounts twice.
Use actual meter readings, separate electricity from gas and compare at least a year for weather-sensitive use. Keep debt repayments and account credit outside consumption cost.
Pre-filled figures are editable, dated reference values with a source.
Frequently asked questions
Will this match my energy bill?
Not necessarily. Regional rates, price changes inside a bill, meter estimates, tariff discounts, debt and rounding can differ.
Does the price cap limit my total bill?
No. It limits rates for covered default tariffs; total cost still rises with energy use.
Sources and review date
Content reviewed on: 2026-08-03.
- GOV.UK – improve home energy efficiency — household efficiency