Electricity Cost Calculator

The short answer

Energy use is watts times hours divided by 1,000, and cost is that figure times your price per kilowatt-hour. A 1,500 W space heater run for 8 hours a day at $0.15 per kWh uses 12 kWh and costs $1.80 a day — about $54 a month if it runs every day. A 60 W bulb left on for the same 8 hours costs 7 cents.

What it depends on

Your price per kWh varies by supplier, tariff and time of use, and the difference between peak and off-peak rates can be several times. Standby and always-on loads — modems, set-top boxes, chargers, game consoles — collectively add up even though each is small. Rated wattage is the maximum rather than the average: a fridge cycles, a heater with a thermostat cycles, and neither runs at full draw continuously.

Where this stops being useful

This is arithmetic on the power and hours you enter. It does not model tariffs, standing charges, taxes or demand charges, and it assumes the rated figure is the actual draw. Your electricity bill shows the rate and the actual consumption for the period. General information only.

A tariff is rarely a flat rate. Most are structured with a fixed daily supply charge, a per-unit energy charge, and sometimes a time-of-use band where evening and weekend rates differ substantially. A calculator that only multiplies units by a single rate will understate a household with a time-of-use plan. Appliances also have a standing load — routers, standby modes, and anything on a 24-hour circuit adds up even when you are not actively using anything.

The most common reason a household cannot account for its electricity bill is a misreading of the tariff rather than a genuine mystery. Pulling the actual bill and identifying the supply charge, the unit rate and any time-of-use band usually explains most of it in a few minutes.

Usage in kilowatt-hours comes from the meter, not from an estimate, so read the meter for a full billing period before deciding anything. Compare that total against the appliance list rather than against a percentage guess. When estimating the effect of a change — replacing a heating system, adding solar — use the calculator with the appliance figures where you have them, and label the result as an estimate. The billing period matters too: a meter read across a partial period gives a misleading annual figure.

Every electrical appliance has a running cost, and it is simply its power consumption multiplied by the time it operates and the price of a unit of electricity. The multiplication is easy once you know two things: a kilowatt is a thousand watts, and a kilowatt-hour is one kilowatt running for one hour, which is the unit on an electricity bill. The power rating is printed on the appliance's label or rating plate, usually in watts or kilowatts. Some devices draw their rating continuously, like a heater or a light, while others cycle on and off, like a fridge or an oven, so the honest way to estimate the cost of a cycling appliance is to measure it with a plug-in energy monitor rather than trusting the plate. For continuously running loads, the calculation is direct: kilowatts times hours gives kilowatt-hours. Comparing appliances this way is genuinely useful. A device rated at 1,500 watts used two hours a day consumes about three kilowatt-hours daily, which at a typical tariff is a noticeable annual figure; a low-power alternative doing the same job can cost a fraction as much over a year. Standby loads deserve the same treatment, because an appliance that draws a few watts around the clock adds up to more than most people expect across a year. This calculator converts the rating and usage into kilowatt-hours per day, month and year, and prices them at your tariff. It assumes the appliance draws its rated power whenever it is on; find your actual tariff on a bill rather than using a national average, and use an energy monitor for anything that cycles. Running the numbers for a few large appliances often shows where the biggest savings lie.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.