Published 14th October 2026
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The calculator on this site works from wattage, and wattage is a good starting point. It is also a maximum. A fridge-freezer, a washing machine or a heater with a thermostat does not draw its label figure all the time, so the real cost is lower than a straight multiplication suggests. A plug-in energy monitor measures what the appliance actually uses, and this article explains how to read it and turn the result into pounds.
The price to use
Under the Ofgem price cap for 1 October to 31 December 2026, electricity on a standard variable tariff paid by direct debit averages 26.32p per kWh, with a standing charge of 54.83p a day. Ofgem says these electricity figures do not include VAT, as the government has removed VAT from electricity bills from 1 October 2026 to 31 March 2027. Gas keeps its 5% VAT. Anyone budgeting beyond March 2027 should check what applies then.
That is a national average for default tariffs. Fixed deals sit outside the cap, and rates vary by region, payment method and tariff type, including Economy 7 and prepayment, so your bill is the better source. Wherever this article says 26.32p, swap in your own figure.
Why the label is not enough
The rating plate gives the most the appliance can draw. For something that runs flat out, such as a kettle or a fan heater on full, that is also what it uses. For anything with a thermostat, a motor cycle or a programme, the average draw is lower, and sometimes much lower.
Three kinds of appliance are worth measuring rather than calculating:
- Anything that cycles. Fridges, freezers and heaters with thermostats switch on and off, so a short reading tells you little.
- Anything with programmes. A washing machine uses most of its power heating water, so a cold wash and a hot wash are very different.
- Anything left on standby. Televisions, consoles, printers and chargers draw a small amount all day, which a label never shows.
How a plug-in monitor works
A plug-in energy monitor sits between the wall socket and the appliance. Its display typically shows the power being drawn right now in watts, and a running total in kilowatt-hours (kWh). Some also show an estimated cost if you enter your unit rate.
It cannot measure anything without a plug. Electric showers, hobs and immersion heaters are wired directly into the mains, so there is nowhere to fit one. For those, wattage from the rating plate and a realistic number of hours is the usual method.
If you need a monitor, Ad a plug-in energy monitor is the term to search for. Look for one that shows both watts and cumulative kWh. For high-power appliances such as a kettle or heater, check that the maximum load printed in the listing covers the wattage on the appliance's label.
A method that gives a usable number
- Plug the appliance into the monitor and the monitor into the wall. Reset the kWh total if there is a reset button.
- Note the watts while it runs. This gives the peak draw and shows how it changes between modes.
- Leave it for a full day, or a full cycle. For a fridge-freezer, 24 hours is the minimum, and a few days is better because the kitchen's temperature changes how often it cycles. For a washing machine, run one complete programme and read the total at the end.
- Read the kWh total. That is the energy the appliance used over the period.
- Multiply by your unit rate. kWh times the rate in pounds gives the cost for the period.
- Scale it up. Multiply by how many days or cycles you expect in a year.
Worked examples
These use invented readings to show the arithmetic. They are not measurements of any product.
- A fridge-freezer that uses 0.7 kWh over 24 hours. 0.7 kWh at 26.32p is about 18.4p a day. Over 365 days that is about £67.25.
- A device on standby drawing 6W all day. 6W is 0.006 kW, so a day uses 0.144 kWh and a year uses 52.56 kWh. At 26.32p that is about £13.83 a year for one device doing nothing.
- A washing machine cycle that uses 1.2 kWh. At 26.32p that is about 31.6p a wash. Three washes a week, 52 weeks a year, is 156 washes and about £49.27.
The standing charge sits outside all of this. At 54.83p a day it comes to about £200.13 over a year, and it is on the bill whether you run anything or not. Measuring helps you cut the part of the bill that responds to what you use.
What to do with the results
The numbers are most useful when they change a decision. A few common outcomes:
- A single appliance that stands out. Compare its measured annual cost with the price of a replacement. A replacement only makes sense if the saving would repay the purchase over a sensible time.
- A set of small standby draws. Several of them in one place, such as a television, a console and a sound system, can go onto Ad a surge-protected extension lead with individual switches, so that one switch turns them all off. Check the lead's rating covers what is plugged in.
- A timer for something that does not need to run all night. Ad A plug-in timer socket switches an appliance off on a schedule without anyone remembering to. Check the appliance is one that is safe to switch off at the wall.
- A smart plug. Ad A smart plug with energy monitoring gives the same readings and also lets you switch the appliance off from a phone. The plug itself uses a little power, so it suits the few appliances you want to track rather than every socket in the house.
Other ways to see your use
A plug-in monitor measures one appliance at a time. If you have a smart meter, its in-home display can show how much the whole house is drawing, and switching things on and off one at a time shows which appliance moves the number. The smart meter article explains what a smart meter does and does not do.
For anything you do not want to measure, the guide and the FAQ list typical wattages, and the calculator will put them into pounds at your own rate.