What the Home Energy Usage Estimator does
This estimator shows where a home's electricity goes, appliance by appliance. For each item it multiplies power by hours of use, days per week and duty cycle, adds the standby power it draws while switched off, and then ranks everything by yearly kWh and share of the total - with the cost at your own tariff.
That is different from the Electricity Cost Calculator, which prices a single power figure. Here the point is the breakdown: the fridge that quietly uses a third of your electricity, the air conditioner that dwarfs everything in summer, and the standby load of boxes that never really switch off.
How to use it
- List your appliances with the wattage from the rating plate or manual, and how many you have.
- Enter the hours each one is on per day and the days per week it is used. A fridge or router is on 24 hours, 7 days.
- Set the duty cycle for appliances that cycle on and off while "on": a fridge compressor typically runs 30-40% of the time, an air conditioner or heater with a thermostat 40-70% depending on the weather. Lights and screens are 100%.
- Enter standby watts for anything left plugged in - set-top boxes, microwaves with clocks, printers, chargers. A plug-in energy meter shows the real figure.
- Enter your price per kWh from your bill to see costs, then sort the table or download the CSV.
Reading the results
The bar chart ranks appliances by yearly energy. Efforts to cut use pay off most at the top of that list, not the bottom.
Standby is counted only for the hours an appliance is not in use, so it never double-counts. Several percent of the total on standby is common in homes with many always-on boxes.
Compare the monthly figure with your bill. If the bill is much higher, something is missing - often electric water or space heating, a second fridge or freezer, or an underestimated air conditioner duty cycle.
Worked example: three appliances, worked by hand
A 150 W fridge is plugged in 24 hours a day, 7 days a week, with the compressor running 35% of the time: 150 x 24 x 7 x 0.35 / 1,000 = 8.82 kWh a week, or 8.82 x 365 / 7 = 459.9 kWh a year.
A 100 W television is on 4 hours a day and draws 1 W on standby for the other 20: 2.8 kWh of viewing plus 0.14 kWh of standby a week. A 500 W washing machine runs 1 hour, 3 days a week, and idles at 2 W for the other 165 hours: 1.5 + 0.33 kWh a week.
The total is 13.59 kWh a week, or about 708.6 kWh a year. The fridge is 8.82 / 13.59 = 64.9% of it, and standby is 0.47 kWh a week (24.5 kWh a year, 3.5%). At 0.30 per kWh the three cost about 212.6 a year.
Formulas and scoring rules
- In-use energy
kWh/week = watts x quantity x hours/day x days/week x duty cycle / 1000- Standby energy
kWh/week = standby watts x quantity x (168 - hours/day x days/week) / 1000- Yearly and monthly
kWh/year = (in use + standby per week) x 365 / 7; month = year / 12; day = year / 365- Share and cost
share = appliance kWh / total kWh; cost = kWh x tariff
How this differs from the Electricity Cost Calculator
The Electricity Cost Calculator answers "what does running this cost?" for one power figure. This estimator answers "which of my appliances uses the most?" by building the whole household from individual items, each with its own hours, days, duty cycle and standby draw, and showing each item's kWh and share of the total. Use the cost calculator for a quick single figure and this one to find where to save.
Limitations: what the result does not prove
- Rated watts are a maximum, not what an appliance draws on average. Duty cycle adjusts for that, but only a plug-in meter or a smart meter gives measured consumption.
- Heating and cooling depend on weather. A single duty cycle is an average; summer and winter months can be very different.
- Tariffs with time-of-use rates, standing charges or tiered blocks are not modelled; the cost uses one flat price per kWh.
- Appliances with variable power - inverter air conditioners, induction hobs, washing machine heating cycles - are only approximated by a single watts figure.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- US DOE Energy Saver - estimating appliance and home electronic energy use - checked 19 Sep 2026
- Lawrence Berkeley National Laboratory - Standby power
Frequently asked questions
How do I find out how much electricity each appliance uses?
Multiply its watts by the hours it runs and divide by 1,000 to get kWh. For appliances that cycle, like fridges and air conditioners, multiply by the share of time the compressor actually runs. A plug-in energy meter measures it directly over a week, which is the most reliable way.
What is a duty cycle?
It is the fraction of time an appliance draws its rated power while it is switched on. A fridge is plugged in all day, but its compressor might only run a third of the time, so its duty cycle is about 33%. Thermostatic heaters and air conditioners behave the same way.
How much electricity does standby use?
Each device is usually small - under 1 W for modern TVs and chargers, several watts for older set-top boxes, printers and games consoles. Together they add up because they draw power 24 hours a day. Ten devices averaging 3 W use about 263 kWh a year.
Which appliances use the most electricity at home?
Usually whatever heats or cools: electric water heaters, space heaters, air conditioners, electric showers and tumble dryers. After those come fridges and freezers because they run all year. Enter your own appliances to see your household's ranking rather than a generic one.
Why does my estimate not match my electricity bill?
Common reasons are a missing appliance, a duty cycle that is too low for heating or cooling in extreme weather, standing charges on the bill, or rated watts that differ from real draw. Adjust the biggest items first; they dominate the total.
How is this different from the Electricity Cost Calculator?
The cost calculator turns one wattage and usage pattern into a cost. This estimator lists every appliance with its own pattern, counts standby separately and shows each item's kWh and share of the household total, so you can see which appliance to tackle first.
Last reviewed by the A2Z.Tools team against the sources listed above.
