Electricity Cost Calculator

How to use this calculator#

1. 1
   Find the appliance's wattageCheck the rating plate on the back or underside, or the label inside the door. If it lists volts and amps instead, multiply them: 120 V × 12.5 A = 1,500 W. Anything showing an annual kWh figure on an energy label is better still — use that directly.
2. 2
   Use average draw for anything that cyclesNameplate wattage is peak, not average. A fridge stamped 150 W runs roughly a third of the time, so it averages nearer 50 W across the day. For fridges, freezers, air conditioners and thermostatic heaters, divide the label's annual kWh by 8,760 to get a true average wattage.
3. 3
   Enter realistic hours, including standbyAn always-on device runs 8,760 hours a year, which is why a 20 W set-top box costs more annually than a 1,000 W microwave. Count seasonal appliances over the months you actually use them, not the whole year.
4. 4
   Take your price per kWh from a real billDivide the energy charge on a recent bill by the kWh used, or read the unit rate printed on it. Keep the daily standing charge out of that figure — it does not change with usage, so folding it in overstates every appliance.
5. 5
   Compare against the alternativesRunning costs only mean something in comparison. Price the LED against the incandescent, the heat-pump dryer against the vented one, and the same appliance shifted onto an off-peak tariff.

The formula#

Watts, kilowatt-hours and your tariff#

A kilowatt-hour is 1,000 watts drawn for one hour, and it is the unit your bill charges for. Divide watts by 1,000 to get kilowatts, multiply by hours of use, then multiply by your price per kWh. A 1,500 W space heater run five hours a day uses 7.5 kWh — at 17 cents that is $1.28 daily and about $38 a month, which is usually the mystery behind a winter bill spike.

Nameplate watts versus what it really draws#

The rating on the label is peak draw, not average. A fridge stamped at 150 W cycles roughly a third of the time, so it averages nearer 50 W across 24 hours. Motor-driven and thermostatic appliances — fridges, freezers, air conditioners, washing machines — all cycle like this. For those, enter an average wattage, or take the annual kWh from the energy label and divide by 8,760.

Standby loads and the cheapest wins#

Always-on devices matter because they run 8,760 hours a year. A games console left in instant-on at 15 W costs about $22 annually; a set-top box at 20 W costs $30. Swapping a 60 W incandescent for a 9 W LED saves roughly $9 a year per bulb at four hours a day. Check whether your tariff has cheaper overnight rates, because shifting the dishwasher and washer can halve those loads.

Worked examples#

Reference tables#

Common mistakes#

• Costing a cycling appliance at its nameplate wattageA fridge stamped 150 W does not draw 150 W for 24 hours — its compressor runs perhaps a third of the time, averaging nearer 50 W. Using the nameplate triples the estimate, turning a $74 annual cost into $223. Use the annual kWh from the energy label divided by 8,760 instead.
• Judging an appliance by its power rating aloneA 3,000 W kettle looks alarming and a 20 W set-top box looks trivial, but the kettle runs 12 minutes a day and the box runs 24 hours. Annual cost: $37 for the kettle, $30 for the box. Energy is power multiplied by time, and time usually wins.
• Folding the standing charge into the unit rateA daily standing charge is a fixed fee for connection and does not vary with consumption. Dividing a whole bill by kWh used inflates the apparent unit rate — badly, in a low-usage home — and makes every appliance look more expensive than it is.
• Treating a published average price as your priceUS residential electricity prices differ by a factor of three between the cheapest and most expensive states, and time-of-use tariffs can differ by that much within a single day. Always calculate on your own unit rate, and check whether shifting a dishwasher or dryer to off-peak halves its cost.

Frequently asked questions#

Key terms#

Watt (W)

The SI unit of power — the rate at which energy is used, equal to one joule per second. It describes how hard an appliance draws, not how much it consumes.

Kilowatt-hour (kWh)

The unit of energy your bill charges for: one kilowatt drawn for one hour, equal to 3.6 megajoules. Ten 100 W bulbs for one hour, or one 100 W bulb for ten hours, both consume 1 kWh.

Nameplate rating

The maximum power draw printed on an appliance's rating plate. For anything thermostatic or motor-driven it is a peak figure, well above the average draw across a day.

Standby (vampire) load

Power drawn by a device that appears to be switched off — typically 1–20 W for anything with a remote, a clock or a network connection. Small individually, it commonly adds 5–10% to a household's annual electricity use.

Standing charge

A fixed daily or monthly fee for being connected to the grid, charged regardless of consumption. It belongs on the bill but not in a per-appliance running cost.

Time-of-use tariff

A rate that changes through the day, with cheaper overnight and off-peak periods. Shifting flexible loads such as dishwashers, laundry and EV charging into those windows can cut their cost substantially.

Sources#