If you want to know how to calculate electricity cost, the answer comes down to one formula: multiply the electricity an appliance uses, measured in kilowatt-hours (kWh), by the price you pay for each kWh. For an appliance rated in watts, the full calculation looks like this:
Electricity cost = (watts ÷ 1,000) × hours used × electricity rate per kWh
Someone usually searches this after seeing a wattage number and wondering what it means in real money. A heater marked "1,500 W" does not tell you much on its own. Once you connect that number to hours of use and your electricity rate, it becomes a cost you can actually understand. That is the whole method. The rest of this guide explains what each part of the formula means, where to find the numbers, and how to turn the result into a daily, monthly, or yearly estimate for any appliance in your home.
What You Need to Calculate Electricity Cost
Three pieces of information are enough for a solid estimate.
1. The appliance wattage
Wattage (W) tells you how much power an appliance draws at a given moment. You can usually find it on the appliance label, in the product specifications, in the owner's manual, or on the manufacturer's website. A space heater might be listed at 1,500 W, while a laptop charger might be 65 W.
Wattage measures power, not the total amount of electricity consumed over time. Power is the rate of use; the total depends on how long the appliance runs. That is why the hours matter in the calculation.
This power-versus-energy distinction is the foundation of every electricity calculation. The U.S. Energy Information Administration explains it the same way: watts measure power at a specific moment, while kilowatt-hours measure how much electricity is used over time. Keep that difference in mind and the rest of the math stays simple.
2. The hours of use
Estimate how many hours per day the appliance actually runs. A heater used on cold evenings might run for three hours. A kettle runs for only a few minutes at a time, while a television might stay on for four or five hours. Be honest about your real habits, because the hours are where most estimates go wrong.
3. The electricity rate per kWh
Your electricity rate is the price your provider charges for one kWh of electricity. It may appear on your bill as something like $0.20/kWh or 20 cents per kWh. On some bills the rate is listed under usage charges; on others you may need to divide the total usage charge by the number of kWh billed to see the effective price.
Use the rate from your own electricity plan or bill, because electricity prices vary widely by country, region, utility, and tariff. No single rate applies everywhere, and some plans charge different rates at different times of day.
The Electricity Cost Formula
The formula has four steps: watts to kilowatts, kilowatts to kWh, and kWh to cost.
Step 1: Convert watts to kilowatts
Electricity is billed in kilowatt-hours, and one kilowatt equals 1,000 watts. Divide the wattage by 1,000:
Watts ÷ 1,000 = kilowatts (kW)
Example: 1,500 W ÷ 1,000 = 1.5 kW
Step 2: Calculate electricity use in kWh
Multiply the kilowatts by the number of hours the appliance runs. This gives you energy use over time:
kW × hours used = kWh
Example: 1.5 kW × 3 hours = 4.5 kWh
A kWh is simply one kilowatt of power used for one hour. It is the unit your utility measures and bills. If you already know an appliance's consumption in kWh from an energy label or a specification sheet, you can skip straight to Step 3.
Step 3: Multiply kWh by your electricity rate
Finally, multiply the kWh by your price per kWh:
kWh × price per kWh = electricity cost
Example: 4.5 kWh × $0.20 = $0.90
Each step builds on the one before it. Watts describe the appliance, hours describe your habits, and the rate describes your electricity plan.
A Simple Electricity Cost Example
Here is the full calculation for one common situation: a 1,500-watt appliance, such as a space heater or a strong hair dryer, used for 3 hours a day. We will use an example electricity rate of $0.20 per kWh. Remember, $0.20/kWh is a hypothetical rate for illustration only. Your real rate may be higher or lower.
Step by step:
- 1,500 W ÷ 1,000 = 1.5 kW
- 1.5 kW × 3 hours = 4.5 kWh per day
- 4.5 kWh × $0.20 = $0.90 per day
So running this appliance for 3 hours a day would add roughly $0.90 per day to the energy side of your electricity costs, based on the assumed rate.
Notice how the number changes meaning at each step. The 1,500 W sounds abstract. The 4.5 kWh describes real daily electricity use. The $0.90 is something you can compare with a coffee, a bus fare, or another appliance.
How to Calculate Daily, Monthly and Yearly Electricity Cost
The same formula works for any time period. You only change the hours.
Electricity cost per hour
For one hour of use, multiply the kilowatts by your rate:
1.5 kW × $0.20 = $0.30 per hour
Electricity cost per day
Multiply the hourly cost by the hours used per day:
$0.30 × 3 hours = $0.90 per day
Electricity cost per month
Multiply the daily cost by the number of days. Assuming 30 days:
$0.90 × 30 = $27 per month
Electricity cost per year
Multiply the daily cost by 365 days:
$0.90 × 365 = $328.50 per year
It also helps to remember what the monthly figure represents. It is not a bill prediction; it is the appliance's share of your energy use, expressed in money. If you run the heater only on weekends, halve the hours and the estimate falls accordingly.
These figures are estimates. They assume the appliance really runs 3 hours every single day at its rated wattage, and they depend entirely on the $0.20 example rate. If your rate is $0.30 per kWh instead, the same appliance costs about $1.35 per day, or around $40.50 per month. This is why plugging in your own electricity price per kWh matters more than any example.
Why Your Calculation May Differ From Your Electricity Bill
An important point: the cost you calculate for one appliance is not the same as the total amount on your household electricity bill.
The basic formula estimates the energy-related cost of the electricity the appliance consumes, using the rate you enter. A real electricity bill can include more than that, depending on your utility and tariff. Depending on where you live, a bill might include fixed charges, supply charges, delivery or network charges, taxes, tiered rates where the price changes after a usage threshold, or time-of-use pricing where the rate depends on the hour.
So if you calculate $27 for a heater and your whole bill is much larger, that does not mean the math is wrong. The bill covers every appliance and device in the home, plus charges that have nothing to do with any single appliance. The formula answers "what does this appliance cost to run?" not "what will my entire bill be?"
Does an Appliance Always Use Its Rated Wattage?
Not always, and this affects how accurate your estimate is.
The wattage on the label is usually a maximum or rated figure. In real use, many appliances draw less power some or most of the time. A refrigerator compressor switches on and off as the thermostat demands. A washing machine heats water at full power but uses far less while spinning. An air conditioner cycles as the room reaches the set temperature. Devices also draw a small amount in standby mode.
For a quick estimate, using the rated wattage is reasonable and keeps the calculation simple. For a more precise figure, look for the appliance's measured energy consumption, such as annual kWh on an energy label, since that reflects real operating patterns better than a single wattage number.
Calculate Your Own Appliance's Electricity Cost
The method works for any appliance you can find a wattage for: a heater, air conditioner, refrigerator, dryer, washing machine, TV, computer, microwave, or electric kettle.
Take the wattage, convert it to kilowatts, multiply by your hours of use, and multiply the result by your electricity rate per kWh. Once you know the appliance's wattage, hours of use, and electricity rate, you can use the Electricity Cost Calculator to work out the estimated running cost without doing the math by hand. It uses the same steps described above, so the result is only as accurate as the numbers you enter.
Keep your own electricity bill nearby. The rate printed there, not any example rate, is the number that makes the calculation real for your household.
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