Electricity Cost Calculator
Running cost of an appliance from its wattage, hours of use and your energy price.
Results update as you type.
About this calculator
An electricity cost calculator turns an appliance’s wattage into money by tracing the chain from power to energy to price. Energy in kilowatt-hours is power in kilowatts times hours of use, so a device’s daily energy is its watts ÷ 1,000, multiplied by the hours it runs each day; the cost is that energy times your price per kWh. Advanced fields let you set the number of identical units and how many days a week they run, so occasional loads are averaged fairly across the calendar.
As a worked example, a 100 W device left on 5 hours a day uses 0.1 kW × 5 = 0.5 kWh daily. At $0.15 per kWh that is about $0.075 a day, which works out to roughly $2.28 a month and $27.40 a year (the tool uses 30.44 days per month and 365.25 days per year for accuracy). A 1,500 W space heater run the same 5 hours costs fifteen times as much — around $1.13 a day — which quickly shows why high-wattage heating dominates a power bill.
The calculator returns the daily, monthly and yearly cost plus the annual energy in kWh, and a period-by-period schedule you can open to compare day, week, month and year. It is the practical way to decide whether an old fridge is worth replacing, budget for a new appliance, spot the phantom cost of always-on devices, or compare the running cost of two products with different wattages.
Frequently asked questions
How is the running cost of an appliance calculated?
Daily energy in kWh is the power in kilowatts (watts ÷ 1000) times the hours it runs per day. Multiply by your price per kWh for the daily cost, then by 30 or 365 for monthly and yearly figures.
How much does a 100 W device cost to run?
At 5 hours a day it uses 0.1 kW × 5 = 0.5 kWh daily. At $0.15 per kWh that is about $0.075 a day, roughly $2.25 a month or $27 a year.
Does standby power count?
Yes — many devices draw a few watts even when off. If you want to include standby, add its wattage over the hours it sits idle, or run a separate calculation for the standby load.
How do I cost several identical appliances at once?
Use the advanced "number of units" field. Ten 10 W bulbs run together cost the same as one 100 W load, so the calculator multiplies the energy by the quantity before applying your price per kWh.
What if the appliance only runs some days of the week?
Set "days used per week" in the advanced options. The tool averages the energy over the full calendar — a device used 5 of 7 days is billed as 5/7 of continuous use — so the monthly and yearly figures stay realistic.
Where do I find an appliance’s wattage?
Check the rating label, nameplate or manual, usually given in watts or as volts and amps (multiply them for watts). For a real-world figure, a plug-in energy monitor measures actual draw, which you can enter directly here.
Why are my monthly and yearly costs not exactly 30 and 365 times the daily cost?
The calculator uses the average calendar month of 30.44 days and year of 365.25 days rather than round 30 and 365, so a $0.075 daily cost becomes about $2.28 a month and $27.40 a year — a touch higher than the rounded estimate.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/electricity/curl
curl "https://calculator.free/api/v1/electricity/?power=100&hours=5&rate=0.15"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/electricity/?" + new URLSearchParams({
"power": "100",
"hours": "5",
"rate": "0.15"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.