Electricity Cost Calculator

What this electricity cost calculator does

Your electricity bill is the sum of every device in the house multiplied by how long it runs and the price your utility charges per kilowatt-hour. This calculator isolates one appliance so you can see what it really costs: whether the space heater in the spare room is worth it, how much a gaming PC adds to the bill, or what charging an electric car at home costs compared with petrol. Enter a wattage and a daily running time, or pick a preset for a typical appliance, and the cost per day, month and year appears instantly.

Watts, kilowatt-hours and the cost formula

Watts (W) measure power, the rate at which a device draws energy. Kilowatt-hours (kWh) measure energy, the amount used over time, and that is what you pay for. The two are linked by running time:

Energy (kWh) = watts × hours ÷ 1,000

Cost = kWh × price per kWh

Example: a 100 W device running 5 hours a day uses 100 × 5 ÷ 1,000 = 0.5 kWh per day. Over a 30-day month that is 0.5 × 30 = 15 kWh, and at $0.17 per kWh it costs 15 × 0.17 = $2.55 per month. Over a year (365 days) it uses 182.5 kWh and costs 182.5 × 0.17 = $31.03. A 1,500 W space heater on for the same 5 hours a day would cost fifteen times as much, about $38 a month.

How to find an appliance's wattage

• The rating label: most appliances carry a plate or sticker near the power cord listing watts, or amps and volts. Multiply amps by volts to get watts (5 A × 120 V = 600 W).
• The manual or product page: look for "rated power" or "power consumption". For TVs and fridges the EnergyGuide or EU energy label gives annual kWh directly, which you can divide by 365 to get daily use.
• A plug-in energy monitor or smart plug: the only reliable way to measure devices that cycle on and off, such as refrigerators, air conditioners and heat pumps. Leave it connected for a full day or week and read the kWh total.
• Standby power: devices that are "off" but still plugged in often draw 0.5 to 10 W around the clock. Enter 24 hours a day to see what that costs.

Remember that the label shows the maximum draw. A 1,000 W microwave only draws that while heating, a washing machine uses most of its energy during the heating and spin phases, and a laptop charger rated 65 W averages far less once the battery is full.

How to use this calculator

1. Choose an appliance from the list to load a typical wattage and daily running time, or leave it on "Custom".
2. Enter the power in watts, or switch to kilowatts for large loads such as an EV charger, water heater or central air.
3. Set the hours of use per day and the days per month. For something that runs continuously, enter 24 hours.
4. Type the price per kWh from your electricity bill. Include delivery and supply charges for an all-in figure.
5. Read the monthly cost in the result panel, then compare it with the other appliances in the table below.

Tips to cut the bill

• Heat is expensive. Anything that makes heat, such as space heaters, dryers, ovens and water heaters, uses 1 to 5 kW. Reducing their running time saves more than switching off every light in the house.
• Swap to LED. A 10 W LED gives the light of a 60 W incandescent bulb, cutting its running cost by over 80%.
• Use a heat pump instead of resistance heating. A heat pump delivers 3 to 4 units of heat per unit of electricity, so the same warmth costs a quarter to a third as much.
• Kill standby power. Smart power strips or simply unplugging rarely-used electronics removes phantom loads that can make up 5 to 10% of household use.
• Shift use to off-peak hours if you are on a time-of-use tariff. Running the dishwasher, washing machine or EV charger overnight can halve what those loads cost.

Limitations

The calculator assumes one flat price per kWh. Many utilities bill in tiers, where the price rises once you pass a monthly threshold, or by time of use, with peak afternoon rates several times the overnight rate. In those cases, enter the rate that applies when the appliance actually runs, or your average all-in price (total bill divided by total kWh) for an overall estimate. Fixed monthly service charges are not included. For the cost of driving, see the fuel cost calculator, and use the unit converter for other energy and power units.