Appliance Wattage & Running Cost Calculator
Enter an appliance’s wattage, how long you use it and your electricity price to see what it really costs to run — per day, week, month and year.
Annual running cost
£460.22
- Cost per day used
- £1.26
- Cost per week
- £8.82
- Cost per month
- £38.35
- Energy per day used (kWh)
- 4.5
- Energy per year (kWh)
- 1,643.63
Energy = power × time. Watts ÷ 1000 gives kilowatts, multiplied by the hours run gives kilowatt-hours (kWh) — the unit electricity is billed in. That energy times your price per kWh is the cost. Yearly figures scale the days-per-week usage across a 365.25-day year.
How to use this calculator
Find the appliance’s power rating in watts (W) — it’s usually on a label near the plug or power inlet, on the rating plate, or in the manual; sometimes it’s given as amps and volts, in which case watts = amps × volts. Enter that wattage, then how many hours you run it on a typical day and how many days a week you use it (leave it at 7 for something used every day). Finally enter your electricity unit rate — the price per kilowatt-hour (kWh) shown on your latest bill. The calculator returns the cost per day used, per week, per month and per year, plus the energy in kWh.
How the calculation works
Electricity is billed by energy, and energy is power multiplied by time. One kilowatt-hour (kWh) is 1000 watts running for one hour. So the calculator divides the wattage by 1000 to get kilowatts, multiplies by the hours per day to get the kWh used on a day the appliance runs, then multiplies by your price per kWh for the daily cost. Weekly cost scales that by the days per week; the annual figure multiplies the weekly energy across a 365.25-day year (which averages in leap years), and the monthly figure is simply the annual cost divided by twelve. Nothing about this depends on where you live — only your unit rate and how much you use the appliance change the answer.
Worked example
A 1500 W appliance used 3 hours a day, every day, at 0.28 per kWh: 1500 ÷ 1000 = 1.5 kW; 1.5 × 3 = 4.5 kWh per day, costing 4.5 × 0.28 = 1.26 a day. Over a week that’s 4.5 × 7 = 31.5 kWh, about 8.82. Across a full year it’s 4.5 × 365.25 = 1,643.6 kWh, roughly 460 a year — or about 38 a month. Halve the daily hours and every figure halves with it.
Frequently asked questions
Where do I find an appliance’s wattage?
Look for a rating label — usually a small metal or printed plate on the back or base of the appliance, near the power cable, or inside the door on things like ovens and washing machines. It will show a figure in watts (W) or kilowatts (kW; 1 kW = 1000 W). If it only lists amps (A) and volts (V), multiply them: watts = amps × volts. The manual or manufacturer’s website usually lists it too. Note that the rated wattage is the maximum draw; motors and heating elements that cycle on and off (fridges, kettles reaching temperature) may average less over time.
What is a kilowatt-hour (kWh)?
A kilowatt-hour is the standard unit of electrical energy and what your supplier charges for. It’s the energy used by a 1000-watt (1 kW) device running for one hour. A 2000 W heater for one hour uses 2 kWh; a 100 W bulb left on for ten hours also uses 1 kWh. Your bill shows a price per kWh (the "unit rate") — multiply the kWh an appliance uses by that rate to get its cost.
Does a higher-wattage appliance always cost more to run?
Not necessarily — running cost is wattage times time. A 2000 W kettle that boils for two minutes uses far less energy than a 40 W broadband router left on 24/7. A high-wattage appliance used briefly can be cheaper than a low-wattage one left on constantly. That’s why this calculator asks for hours of use as well as wattage: it’s the combination that determines the bill.
Why use 365.25 days for the yearly figure?
A calendar year is not exactly 365 days — leap years add a day every four years, giving an average of 365.25 days per year. Using that average makes the annual estimate slightly more accurate over the long run than a flat 365. The difference is tiny (about 0.07%), so for a single year you can treat the annual figure as "roughly what a year costs" either way.
Is standby power included?
No — this works out the cost while the appliance is actively running for the hours you enter. Many devices also draw a small "standby" or "vampire" load when switched off but plugged in (often 0.5–3 W). If you want to include that, run the calculator a second time with the standby wattage and 24 hours a day, then add the two results. For most single appliances the active running cost dominates.
Will the cost match my electricity bill exactly?
It’s a close estimate, not a metered reading. Real usage varies: thermostatic appliances cycle on and off, actual run-time differs from your estimate, and some tariffs add a daily standing charge or charge different rates at different times of day. Use realistic average hours and your correct unit rate and the figure will be in the right ballpark — good enough to compare appliances or decide whether something is worth switching off.