This hub helps you turn the wattage printed on an appliance into a practical estimate of what it costs to run. The important point is that wattage alone is not a cost: you also need to know how long the appliance runs and the electricity unit rate you pay in pence per kilowatt-hour (kWh). Warmer Bills uses stated numbers, units, assumptions and dates so that the calculation can be checked rather than taken on trust.
Wattage is not the same as running cost
An appliance label might show a figure in watts, such as its rated electrical power. That tells you about the rate at which the appliance can use electricity, but it does not tell you how many pounds or pence it will add to your bill.
To estimate the running cost, you need three pieces of information: the appliance wattage, the amount of time it operates and your electricity unit rate. You should also remember that a rated wattage does not necessarily mean the appliance draws that maximum power continuously. Thermostats, cycles, compressors and different operating modes can all change actual consumption.
Where to find the wattage of an appliance
Look for the rating plate, product label or technical information printed on the appliance. You are looking for a figure marked in watts, usually shown as W. Some appliances may instead show power in kilowatts, written as kW.
| Appliance | Where to check | What number to look for |
|---|---|---|
| Tumble dryer | Check the rating plate around the door opening, rear panel or another manufacturer label on the machine. | A power rating shown in W or kW. |
| Portable heater | Look on the rear, underside or manufacturer label near the controls or power cable. | The rated heating power in W or kW. |
| Kettle | Check the base, underside of the kettle or its rating label. | The electrical power rating in W or kW. |
| Fridge | Look inside the cabinet, around the door frame, on a side wall or on a label at the rear. | A power rating in W, where supplied. For annual consumption estimates, also check any stated kWh figure. |
The running-cost calculation
The basic calculation is:
wattage ÷ 1,000 × hours used × unit rate
Watts measure electrical power. Dividing watts by 1,000 converts them into kilowatts. Multiplying kilowatts by the number of hours used gives energy consumption in kilowatt-hours, or kWh. Your tariff then charges a number of pence per kWh for that energy.
If your electricity unit rate is stated in pence per kWh, the result of the calculation is in pence. Divide by 100 if you want to express it in pounds. Use the unit rate shown on your own tariff or bill, together with the date that rate applies. An illustrative rate should never be treated as a live Ofgem or supplier rate.
One hour versus eight hours
One hour
For an appliance rated at W watts, running for one hour, the energy calculation is W ÷ 1,000 × 1. Multiply that result by your unit rate to estimate the cost.
Eight hours
At the same wattage and the same unit rate, eight hours of operation uses eight times as much energy as one hour. The estimated usage cost is therefore also eight times higher.
This is why operating time matters so much. A device with a modest-looking hourly cost can become significant when it runs for many hours each day, while a high-power appliance used briefly may have a very different overall impact.
Standing charge is separate
Your appliance calculation covers usage charged through the electricity unit rate. The standing charge is different. It is a fixed daily charge associated with having the energy supply available and is normally payable regardless of whether a particular appliance is switched on.
Standing charge can therefore form a meaningful fixed part of a household bill even when appliance use is reduced. Giving a numerical percentage of a typical bill would require both a stated standing-charge rate and an assumed level of household energy consumption, so there is no single percentage that can be quoted responsibly without those assumptions.
Appliances people can underestimate
Some costs are easy to misjudge because either the power is high or the operating time is long. High-power portable electric heaters can add usage quickly while they are drawing full power. Tumble dryers can also use substantial amounts of electricity during a cycle. At the other end of the scale, appliances and devices left operating for many hours can accumulate a meaningful cost even when their hourly figure initially looks small.
The useful comparison is not simply which appliance has the largest wattage. Consider wattage, actual operating behaviour and the number of hours or cycles involved.
Use your own tariff for the most useful estimate
For a household-specific calculation, take the electricity unit rate from your latest tariff information or bill and note the date it applies. Then combine it with the appliance’s stated power and a realistic estimate of how long it operates. Where an appliance switches itself on and off rather than drawing its rated power continuously, a measured or manufacturer-stated energy-consumption figure may give a better estimate than simply multiplying the maximum wattage by the full elapsed time.
Find appliance running-cost guides
Warmer Bills adds individual appliance cost guides as they are published. Each guide is intended to show the numbers, units, assumptions and applicable rate date behind the estimate rather than relying on vague claims about whether an appliance is expensive to run.