Electricity Cost Calculator

How to Use the Electricity Cost Calculator

Everything on an electricity bill reduces to one unit: the kilowatt-hour, which is a thousand watts drawn for one hour. Once you can convert an appliance into kilowatt-hours, the cost of running anything becomes arithmetic rather than guesswork.

1. Find the power draw. It is on the rating label, usually on the back or underneath, in watts or kilowatts. A plug-in energy meter gives a much better figure for anything that cycles, and costs less than one month of being wrong.
2. Enter the hours a day and days a week. Be honest rather than generous — a heater on for four hours costs a third more than one on for three, and that is the whole calculation.
3. Put in your unit rate. It is on the bill, usually per kilowatt-hour. Standing charges are separate and are not included here, since they do not vary with what you plug in.
4. Adjust the carbon intensity if you know it. The default of 0.371 kg per kWh is close to the US grid average; France sits near 0.06 and coal-heavy grids exceed 0.7.

All of this runs locally in your browser. No details about your household are transmitted or stored.

Electricity Cost Formula

One conversion and three multiplications. The only subtlety is dividing by a thousand at the right moment.

The rating label is the honest starting point but it is a maximum, not an average. Anything with a thermostat — a fridge, a heater, an air conditioner, an electric kettle held at temperature — cycles on and off, and its average draw over a day can be a third of its nameplate figure or less.

That is why a plug-in energy meter is worth the small cost for anything you are seriously investigating. It measures actual kilowatt-hours over a week and removes every assumption on this page except the price.

Example

Worked example one: a 1,500 W space heater, 3 hours a day, every day. The draw in kilowatts is 1,500 ÷ 1,000 = 1.5 kW. Over three hours that is 1.5 × 3 = 4.5 kWh a day. At $0.17 a kilowatt-hour, the cost is 4.5 × 0.17 = $0.765 a day.

Scaling up: $5.36 a week, 4.5 × 30.4375 × 0.17 = $23.28 a month, and 4.5 × 365 × 0.17 = $279.23 a year. That is 1,642.5 kilowatt-hours annually, which at 0.371 kg of carbon per kWh is 609 kg of CO₂ — well over half a tonne from one appliance used three hours a day.

Worked example two: the same heater five days a week. The duty factor becomes 5 ÷ 7 = 0.7143, so the daily average falls to 4.5 × 0.7143 = 3.214 kWh. The yearly total drops to 1,173.2 kWh and $199.45 — a saving of $79.78, or 28.6%, for switching it off at weekends.

For contrast, consider replacing a 60 W incandescent bulb used five hours a day with a 9 W LED. The old bulb uses 0.30 kWh a day and costs $18.62 a year; the LED uses 0.045 and costs $2.79. The saving is $15.82 a year per bulb — real, but a fifth of what turning the heater off at weekends achieves. Big loads used for hours are where the money is.

Reading the Yearly Figure

The yearly figure is the one that changes behaviour, and that is deliberate. Seventy-six cents a day sounds like nothing; $279 a year sounds like a decision. Both describe the same heater, and the second framing is the one that makes it comparable with the cost of insulating the room instead.

Watts times hours is the whole story, and it explains why intuition about energy so often misleads. A 3,000 W tumble dryer feels like the expensive appliance, but used one hour a day it costs less annually than a 150 W fridge that never switches off. Duration beats power far more often than people expect.

That is also why standby power matters less than its reputation suggests. A device drawing 5 W continuously uses 43.8 kWh a year, or about $7.45. Worth eliminating across a dozen devices; not worth reorganising your life around when a single heating decision is worth forty times more.

The carbon figure and the cost figure move together, because both are driven by kilowatt-hours. What differs is the multiplier: at 0.371 kg per kWh this heater emits 609 kg a year, but on the French grid at roughly 0.06 it would emit under 100 kg for identical use. Where the electricity comes from matters as much as how much you use.

For the wider household picture, the budget calculator puts utilities alongside everything else, and the percentage calculator is useful for working out what a tariff change actually does to a bill.

Five Reasons Your Bill Differs

Five reasons your bill will not match this figure exactly.

Nameplate against actual draw. Rating labels state maximum consumption. Anything thermostatically controlled spends most of its time drawing far less, so a nameplate estimate for a fridge or an air conditioner can be double the truth. A plug meter settles it.

Tiered and time-of-use tariffs. Many suppliers charge more above a monthly threshold, or vary the rate by hour of the day. Running a dryer at three in the afternoon and at three in the morning can cost meaningfully different amounts on the same tariff.

Standing charges. Most bills carry a fixed daily charge for being connected at all, independent of consumption. It is excluded here because it does not change when you unplug something — but it does mean your bill is always higher than the sum of your appliances.

Seasonal use. A space heater used three hours a day for four months costs a third of what this yearly figure suggests, and an air conditioner is the same story in reverse. For seasonal appliances, read the monthly figure and multiply by the months you actually use it.

Grid intensity moves constantly. Carbon per kilowatt-hour varies by country, by season and by hour, since the generation mix changes with demand and weather. The single figure used here is an annual average, and the real number at any given moment can be half or double it.