Appliance usage
Use the appliance wattage from its label or manual and your current tariff rate for the most accurate estimate.
Know your usage. Cut your costs.
Use the appliance wattage from its label or manual and your current tariff rate for the most accurate estimate.
UNDERSTAND THE TOOL
Your electricity bill is based on the energy your appliances consume over time, measured in kilowatt-hours (kWh). Watt Wise converts an appliance's wattage into a daily, monthly and annual running cost using the unit rate from your tariff. It is designed to be quick and straightforward: enter three values, click Calculate, and see the numbers laid out clearly.
Whether you are comparing a new heat pump to your old boiler, trying to understand why your bill is higher in winter, or simply curious what it costs to leave a television on standby, this calculator gives you a reliable starting point without needing a spreadsheet.
Watt Wise divides the appliance's rated wattage by 1,000 to convert it to kilowatts, multiplies by daily hours of use to get kWh per day, and then multiplies by the unit rate in pence. Weekly usage patterns are taken into account when projecting monthly and annual figures, so the results reflect realistic use rather than assuming every day is identical.
An appliance's rated wattage is its maximum power draw. In practice, many devices use considerably less. Thermostatically controlled appliances such as fridges and washing machines cycle on and off, so their average consumption is lower than the label suggests. Variable-speed devices like laptop chargers also draw different amounts depending on load. For those appliances, the calculator gives a useful upper-bound estimate rather than a precise reading.
A 2,000 W electric shower used for 10 minutes each morning uses roughly 0.33 kWh per day. At 28 pence per kWh that costs about 9 pence per shower — around £2.80 per month for one person. Two people in the household doubles that estimate to about £5.60 per month, or roughly £67 per year, before standing charges.
Your electricity unit rate appears on your bill, usually expressed in pence per kWh. It may also appear in your energy supplier's app or online account. The Ofgem price cap sets a maximum rate per kWh each quarter; checking the current cap is a useful cross-reference if your bill looks unusually high. Economy 7 and Economy 10 tariffs have separate day and night rates, so you may want to run the calculator twice for appliances that operate at different times.
Watts measure the rate at which an appliance uses power right now. Kilowatt-hours measure the total energy used over time. A 1,000 W appliance running for one hour uses 1 kWh. Your bill charges you per kWh consumed, not per watt.
No. The standing charge is a fixed daily cost that appears on your bill regardless of how much electricity you use. It is separate from the unit rate and should be added on top of these estimates when working out your total bill.
The wattage is usually printed on a label on the appliance itself, on the plug or power adaptor, or in the product manual. If you cannot find it, a smart plug with an energy monitor can measure the actual draw directly.
A fridge's compressor does not run continuously. It cycles on and off to maintain temperature, so actual consumption is often 30–50% lower than rated wattage multiplied by 24 hours would imply. Energy labels on appliances give a more realistic annual consumption figure for comparison.
This calculator covers electricity only. Gas is billed in kWh too but at a different unit rate, so you would need to compare the two rates separately and also account for appliance efficiency ratings.
Yes. The same kWh unit applies to both consumption and generation. If your panels generate an estimated 3 kWh on a sunny day, you can directly compare that against the consumption figures this calculator produces to see how much of your usage could be offset.