Energy Cost
Work out what an appliance or circuit really costs to run — from its power rating and hours of use, from two meter readings, or by comparing two options to see the yearly saving and how long a replacement takes to pay for itself. Uses your Settings currency, fully offline.
Open Energy Cost →What is the energy cost calculator?
A free electricity cost calculator that runs entirely in your browser. It answers the same question three ways. Enter an appliance's power rating and how long it runs and you get the energy it uses and what it costs per day, week, month and year, including any daily standing charge and, if you supply your grid's carbon intensity, the carbon dioxide behind it. Enter two meter readings and the days between them and you get the units used, the bill for that period split into energy and standing charge, the daily average, the average continuous power and a projection over a full year. Or compare two appliances side by side — an old bulb against an LED, say — to see the yearly saving and how long a replacement takes to pay for itself. Prices use the currency from your Settings, and every figure stays on your device.
How to use Energy Cost
- Pick a tab — Running cost for an appliance you know the rating of, From meter readings for a real bill, or Compare two to weigh up a replacement.
- Enter the usage — Type the power in watts, the hours it runs each day and how many days a week. A 2 kW heater on for 3 hours a day is 2000, 3 and 7.
- Add your tariff — Enter the price per kWh from your bill, plus the daily standing charge if you have one. Leave the standing charge blank to see the running cost alone.
- Read the totals — Cost and kWh appear per day, month and year. On the Compare tab, add what the switch would cost to see the payback time.
Frequently asked questions
Where do I find the price per kWh?
It is on your electricity bill, usually called the unit rate. Enter it in the same currency your Settings are set to — for example 0.30 for thirty pence or cents a unit.
How is the yearly figure worked out?
From 365.25 days a year, which is 52.1786 weeks, so leap years are included. Monthly is the yearly figure divided by twelve rather than a fixed four weeks, which is why it looks slightly higher than four times the weekly cost.
What does the average continuous power mean?
On the meter tab, it is the steady wattage that would have used the same units over the same period. It is a useful sanity check — a house averaging 400 W between readings is behaving very differently from one averaging 2 kW.
Why do I have to enter the carbon intensity myself?
Because it varies enormously by country, by grid and by year, and it changes as generation changes. Rather than assume a figure that might be badly wrong for you, the tool leaves it blank and only shows carbon dioxide when you supply a number.
Tips
- For an appliance that cycles, such as a fridge or a heater on a thermostat, estimate the hours it actually runs rather than the hours it is switched on.
- The standing charge is per calendar day whether you use anything or not, so it inflates the cost of a rarely used appliance if you include it.
- Compare mode works for any pair of options with the same usage pattern — bulbs, pumps, kettles or old versus new white goods.