Skip to content
xmoo.app

Tool · Electrical

Electricity Cost Calculator

What does a device cost to run for a year? Enter its power, how long it runs and its standby power, plus your electricity price – and get energy use and cost per day, month and year.

Empty or 0 if the device is otherwise fully unplugged.

Ofgem, Oct–Dec 2026 (what this means)

Energy per year
Cost per year
per month
·
per day
·
of which standby per year

      

    


    
What it is for

    

    
How the tool calculates

    
Power in watts (W) says how much energy a device converts per unit of time –
      one watt is one joule per second. Power times time gives energy, here in
      watt-hours (Wh). The prefix “kilo” stands for a thousand, so a kilowatt-hour (kWh) is
      1,000 Wh. Electricity suppliers bill by the kilowatt-hour – it is the “unit” on a UK
      bill.

    
The tool works over a week, so that devices that only run on some days fit as well:

    
    
      
  1. Running hours per week = hours per day × days per week
    2. 
      
  2. Standby hours per week = 168 h (7 × 24) − running hours
    3. 
      
  3. kWh per week = (running power × running hours + standby power × standby hours) ÷ 1,000
    4. 
      
  4. kWh per year = kWh per week × 365 ÷ 7; per month one twelfth of that, per day one 365th
    5. 
      
  5. Cost = kWh × price per kWh (in pence, cents or Rappen ÷ 100)
    6. 
    

    
The tool assumes 365 days a year and ignores leap years.


    
Worked example

    
A television with these example values (they are already in the calculator when it opens):
      80 W when on, 4 hours a day, every day, 0.5 W on standby. As the price we use the
      Ofgem price cap of 26.32 p/kWh.

    
    
      
  1. Running: 4 h × 7 = 28 h per week, standby: 168 h − 28 h = 140 h
    2. 
      
  2. Week: (80 W × 28 h + 0.5 W × 140 h) ÷ 1,000 = (2,240 + 70) ÷ 1,000 = 2.31 kWh
    3. 
      
  3. Year: 2.31 kWh × 365 ÷ 7 ≈ 120.45 kWh
    4. 
      
  4. Cost: 120.45 kWh × 26.32 p ÷ 100 ≈ £31.70 a year, of which
        standby is about 3.65 kWh or £0.96
    5. 
    

    

      
        Time per week: 168 hours
        
        
        28 h
        Standby 140 h
        Energy per week: 2,310 Wh
        
        
        On: 80 W × 28 h = 2,240 Wh
        
        Standby: 0.5 W × 140 h = 70 Wh
        2.31 kWh per week × 365 ÷ 7 ≈ 120.45 kWh a year
        Standby lasts five times as long as running, but is only 3 % of the energy.
      
      
The example as a picture: standby fills most of the week but only a small part of the energy. Own illustration.

    

    
The values are a worked example, not figures for a particular device. What your television
      uses is on its rating plate or datasheet – or you measure it (see below).


    
Which electricity price to enter

    
The most accurate is your own unit rate per kilowatt-hour – it is in your
      contract and on your bill. A daily or monthly standing charge is due whatever you
      use and does not belong in this calculation: it does not change when you use a device more or
      less.

    
If you do not have your price to hand, pick your country and the button fills in an official
      average. For 42 countries the tool knows one, in the local currency. The sources
      do not all measure the same thing:

    
    
Canada and Australia publish prices only by province or region, and for most other countries
      there is no free official figure. Choose “Other country” and enter your own price – the result
      is then shown without a currency symbol.


    
Rating plate or real consumption?

    
The rating plate usually shows the rated or maximum power. Many devices do not
      draw that all the time:

    
    
For devices like these, measuring beats guessing. A plug-in energy monitor sits
      between the socket and the device and counts the kilowatt-hours used. Leave it in for a whole
      week, then work out the average power: measured kWh × 1,000 ÷ 168 h. Enter that as the
      power, with 24 hours and 7 days and no standby – it is already included in the
      measurement.


    
Measuring and cutting standby

    
Many devices are never fully off: the power supply, the remote-control receiver or the network
      connection stay live. You measure that with the same plug-in monitor while the device is switched
      off. Check the monitor’s datasheet for the smallest load it measures accurately – very small values
      are below that on some models.

    
The easiest way to cut it is an extension lead with individual switches: TV,
      soundbar and games console on one lead, off together with one switch. Do not switch off devices
      that still work on standby – the router, a recorder with a scheduled recording or devices that
      download updates overnight.


    
Limits of this tool

    

    
Privacy: the calculator runs entirely in your browser. What you enter is not
      sent to xmoo.app or anyone else.


    
Sources

    
    
Page last updated: 31 October 2026