Electricity Cost Calculator
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Cost for the period
- Cost per year at this usage
- $745
- Cost per day
- $2.04
- Cost per hour
- $0.2550
- Energy used
- 360 kWh over 30 days
- Power draw used
- 1,500 W (1.5 kW)
- At 1500 W and 8 hours a day this uses 12 kWh daily. The arithmetic is only ever watts ÷ 1,000 × hours × rate — everything else is choosing honest inputs.
- A 1500 W load running 8 hours a day costs $744.60 a year. High-wattage resistive appliances — space heaters, water heaters, dryers — dominate a bill in a way that lighting and electronics cannot, because the wattage is one to two orders of magnitude higher.
Common appliances at your rate and hours
Every row assumes 8 hours a day at $0.17 per kWh. Wattage is what separates them, and it varies by two orders of magnitude.
| Appliance | Watts | Per day | Per year |
|---|---|---|---|
| LED bulb | 10 | $0.01 | $5 |
| Laptop | 65 | $0.09 | $32 |
| Refrigerator (running) | 150 | $0.20 | $74 |
| Desktop PC + monitor | 250 | $0.34 | $124 |
| Window air conditioner | 900 | $1.22 | $447 |
| Space heater | 1,500 | $2.04 | $745 |
| Clothes dryer | 3,000 | $4.08 | $1,489 |
| Electric water heater | 4,000 | $5.44 | $1,986 |
The same appliance at different daily use
| Hours a day | kWh a year | Cost a year |
|---|---|---|
| 1 | 548 | $93 |
| 2 | 1,095 | $186 |
| 4 | 2,190 | $372 |
| 8 (yours) | 4,380 | $745 |
| 12 | 6,570 | $1,117 |
| 24 | 13,140 | $2,234 |
How do you calculate the cost of running an appliance?
Divide the appliance's wattage by 1,000 to get kilowatts, multiply by hours used, then multiply by your rate per kilowatt-hour. A 1,500 W space heater run 8 hours a day for 30 days uses 360 kWh and costs $61.20 at 17 cents.
cost = (watts ÷ 1,000) × hours × rate per kWh watts = amps × volts- watts
- Power draw from the nameplate, while running
- ÷ 1,000
- Converts watts to kilowatts, the billing unit
- hours
- Actual running time, not time switched on
- rate
- Your cost per kilowatt-hour, from your bill
Electricity is billed by the kilowatt-hour, which is one kilowatt drawn for one hour. So the whole calculation is a unit conversion and two multiplications, and the arithmetic is never the hard part. Getting a useful answer depends entirely on two honest inputs. The first is running hours rather than hours switched on: a refrigerator is plugged in 24 hours a day but its compressor runs perhaps eight, and a thermostatic space heater at its setpoint cycles rather than drawing full power continuously. Using 24 hours where 8 is correct overstates the cost threefold. The second is your true rate. The headline energy charge on a bill excludes delivery, transmission, demand and fixed charges, and dividing the total bill by the kWh used often gives a figure 30 to 60 percent higher. Use that all-in number. Where the nameplate gives amps instead of watts, multiply by the voltage — 120 V on a standard US outlet, 240 V for a dryer or range.
- Find the appliance's wattage on its nameplate or label.
- Divide the wattage by 1,000 to convert it to kilowatts.
- Multiply by the hours it actually runs, not hours switched on.
- Multiply by your rate per kilowatt-hour from the bill.
- Multiply by the number of days for a monthly or annual figure.
Worked example: A 1,500 W space heater run 8 hours a day for 30 days at $0.17 per kWh
A 1,500 W space heater run 8 hours a day for 30 days at $0.17 per kWh
The heater draws 1,500 W, which is 1.5 kW. Running 8 hours a day uses 1.5 × 8 = 12 kWh daily, so over 30 days it is 360 kWh. At 17 cents that comes to $61.20 for the month, or $0.255 for every hour it runs. Extended across a full year at the same usage it is 4,380 kWh and $744.60 — from one appliance. The comparison that makes the point is a 10 W LED bulb on the same 8 hours a day: 29.2 kWh and $4.96 a year, which is 150 times less for 150 times less wattage. That ratio is the whole lesson of an electricity bill. High-wattage resistive heat — space heaters, water heaters, dryers — dominates consumption, and no amount of attention to lighting or electronics can offset it. Note too that 1,500 W at 120 V is 12.5 amps, which is most of a 15-amp circuit.
What each electricity cost input means
- How is the appliance rated?
- Nameplates give one or the other. Watts = amps × volts, so either works.
- Power draw
- From the appliance's nameplate or label. This is the draw while running, not an average over the day.
- Current
- Used instead of watts when the nameplate gives amps.
- Voltage
- 120 V for a standard US outlet, 240 V for a dryer, range or EV charger.
- Hours used per day
- Actual running time, not time switched on. A thermostat-controlled appliance cycles, so it runs far less than it is on.
- Days used
- Days in the period you are costing. Thirty for a month, 365 for a year.
- Electricity rate
- Your cost per kilowatt-hour, from your bill. Divide the total bill by the kWh used to get your true all-in rate, which is usually higher than the headline energy charge.
- Standby draw
- What it draws while off but plugged in. Small per device, but it runs 24 hours a day — which is the point.
What this electricity cost does not account for
- Use actual running hours, not hours switched on. A refrigerator is plugged in continuously but its compressor runs roughly a third of the time, and a thermostatic heater cycles once the room reaches temperature.
- Nameplate wattage is the maximum draw. Appliances with motors or variable output average less, sometimes much less, so the result is an upper bound for those.
- Your true rate is higher than the headline energy charge. Delivery, transmission and fixed charges often add 30% to 60% — divide your total bill by the kWh used instead.
- Tiered and time-of-use tariffs charge different rates by consumption band or hour of day. A single average rate cannot capture either, and peak rates can be several times off-peak.
- Standby power is small per device but runs 24 hours a day. A few watts each across dozens of devices is a measurable share of a household bill.
- Heating and cooling are not simple resistive loads. A heat pump moves two to four times more heat energy than it consumes in electricity, so its wattage understates its output.
- Where the nameplate gives amps, multiply by the actual supply voltage. Using 120 V for a 240 V appliance halves the answer.
Frequently asked questions
How much does it cost to run a 1,500 W space heater?
About $0.255 an hour at 17 cents per kWh. Run 8 hours a day that is $2.04 daily, $61.20 a month and $744.60 a year — enough to dominate a winter electricity bill on its own.
How do you convert watts to kilowatt-hours?
Divide the watts by 1,000 to get kilowatts, then multiply by the hours of use. A 1,500 W appliance for 8 hours is 1.5 × 8 = 12 kWh.
What is the average cost per kWh?
US residential rates vary widely by state, roughly 11 to 45 cents per kWh. Use your own bill rather than an average — divide the total by the kWh consumed to capture delivery and fixed charges.
How do I find watts if the label only shows amps?
Multiply amps by volts. A 12.5 A appliance on a 120 V outlet draws 1,500 W. Use 240 V for a dryer, range, EV charger or anything on a double-pole breaker.
Does standby power actually matter?
Per device, barely. A 2 W standby draw costs about $3 a year. The reason it adds up is that it runs 24 hours a day across dozens of devices in a typical home.
Which appliances use the most electricity?
Anything producing resistive heat — water heaters, space heaters, clothes dryers, ovens — because their wattage is one to two orders of magnitude above lighting and electronics. Air conditioning follows closely in summer.
Sources and review
- Electricity explained: factors affecting electricity prices — U.S. Energy Information Administration
Last reviewed .