watt Electricity Cost Calculator, Estimate the Running Cost of Any Appliance
By Shihab Mia · Reviewed by Shihab Mia, ToolNimba Founder and Editor · Updated 2026-07-12
This calculator gives estimates for general budgeting and education only. Your actual cost depends on your local rate structure, taxes, and how each appliance behaves. Always check your own utility bill for exact figures.
Monthly figure uses a 30-day month. A calendar-average month (30.44 days) would be slightly higher.
Typical appliance wattages
| Appliance | Typical power | Cost per hour at 0.15/kWh |
|---|
An electricity cost calculator tells you what an appliance costs to run from three numbers: its power in watts, how many hours a day you use it, and your electricity rate in dollars per kWh. It converts watts to kilowatt-hours, multiplies by your rate, and shows the energy used and the cost for a day, a month, and a year in one view. Everything is computed in your browser, so nothing you type is uploaded.
What is the Electricity Cost Calculator?
Your electric bill is charged by the kilowatt-hour (kWh), which is the energy used by a 1,000-watt device running for one hour. To turn an appliance nameplate into money you only need to bridge two gaps: convert its power from watts to kilowatts by dividing by 1,000, and multiply by the number of hours it actually runs to get kilowatt-hours. Multiply those kilowatt-hours by the price per kWh printed on your bill and you have the cost. This tool does exactly that and then scales the daily figure up to a month and a year so the impact is easy to see.
The daily energy is watts divided by 1,000, times hours per day. A 1,500-watt space heater on for 3 hours uses 1.5 kW times 3 hours, which is 4.5 kWh a day. At a rate of 0.15 dollars per kWh that is 4.5 times 0.15, or 0.675 dollars a day. From there the monthly cost is the daily cost times 30 and the yearly cost is the daily cost times 365, giving about 20.25 dollars a month and 246.38 dollars a year for that one heater. Seeing the annual number is what turns a "cheap" gadget into an obvious budget line item.
Two inputs decide almost everything, so it is worth getting them right. The first is real running hours, not hours the device is plugged in. A refrigerator is connected 24 hours a day but its compressor cycles on and off, so its average continuous draw is a fraction of its peak; that is why we list it at roughly 150 W average rather than its startup surge. The second is your true rate. Look for the total price per kWh on your bill, including delivery and taxes, not just the supply charge, because the delivery portion is often as large as the energy portion. If your utility uses tiered or time-of-use pricing, run the calculator once per rate band to see the range.
Use the built-in appliance list to load a typical wattage fast, then adjust the hours to match your habits. The wattages shown are representative averages: an LED bulb around 10 W, a laptop around 50 W, a TV around 100 W, a fridge around 150 W average, a microwave around 1,000 W, an AC window unit around 1,200 W, a space heater around 1,500 W, and an electric oven around 2,400 W. Your own appliance may differ, so for the most accurate result read the watts (or amps times volts) from its label or a plug-in power meter and type that in.
Do not forget standby, or "vampire", power. Many devices keep drawing a few watts even when switched off or idle: TVs, game consoles, cable boxes, chargers left in the wall, microwaves with a clock, and smart speakers. Any one of them is small, but a typical home runs dozens of them around the clock, and the U.S. Department of Energy estimates idle loads can account for a meaningful slice of an average bill. To include a standby load here, enter its idle wattage (often 1 to 10 W) and 24 hours a day, and the yearly figure will show whether a switched power strip is worth it.
Context helps you judge the result. The U.S. residential average price is roughly 16 to 17 cents per kWh according to the Energy Information Administration, but state rates range from under 12 cents to well over 30 cents, so your own rate matters far more than any national figure. Two levers cut cost: lower watts (an LED instead of an incandescent bulb, an ENERGY STAR appliance instead of an old one) and fewer hours (a timer, a thermostat setback, or simply switching things off). Because cost is watts times hours, a high-wattage device used briefly can be cheaper than a modest device left on all day, which is why comparing appliances on wattage alone is misleading.
When to use it
- Deciding whether a space heater, portable AC, or dehumidifier is worth running for long stretches.
- Comparing the yearly cost of an old appliance against a lower-wattage replacement before you buy.
- Estimating what a gaming PC, mining rig, or always-on server adds to your monthly bill.
- Checking how much a single always-on device like a router, fish tank, or standby TV costs over a year.
- Budgeting seasonal heating or cooling by trying different daily-hour and rate scenarios.
- Explaining to a housemate or tenant how a specific appliance affects the shared electricity bill.
How to use the Electricity Cost Calculator
- Enter the appliance power in watts, or pick a typical appliance from the dropdown to fill it for you.
- Type how many hours per day you actually run it (use average running hours, not hours plugged in).
- Enter your electricity rate in dollars per kWh from your bill (the default is 0.15).
- Read the energy used per day and the cost per day, month, and year in the result boxes.
- Use Copy result to grab the numbers, and try different hours or rates to compare scenarios.
Formula & method
Worked examples
A 1,500 W space heater running 3 hours a day at 0.15 dollars per kWh (the defaults).
- Convert power to kilowatts: 1500 / 1000 = 1.5 kW.
- Energy per day: 1.5 kW x 3 hours = 4.5 kWh.
- Cost per day: 4.5 kWh x 0.15 = 0.675 dollars.
- Cost per month: 0.675 x 30 = 20.25 dollars.
- Cost per year: 0.675 x 365 = 246.38 dollars.
Result: About 4.5 kWh and 0.68 dollars a day, 20.25 dollars a month, and 246.38 dollars a year.
A 10 W LED bulb left on 5 hours a day at a higher 0.22 dollars per kWh rate.
- Convert power to kilowatts: 10 / 1000 = 0.01 kW.
- Energy per day: 0.01 kW x 5 hours = 0.05 kWh.
- Cost per day: 0.05 kWh x 0.22 = 0.011 dollars.
- Cost per year: 0.011 x 365 = 4.02 dollars.
Result: About 0.05 kWh and roughly 1 cent a day, which is only about 4.02 dollars a year.
A 1,200 W window air conditioner running 8 hours a day through summer at 0.18 dollars per kWh.
- Convert power to kilowatts: 1200 / 1000 = 1.2 kW.
- Energy per day: 1.2 kW x 8 hours = 9.6 kWh.
- Cost per day: 9.6 kWh x 0.18 = 1.728 dollars.
- Cost per month: 1.728 x 30 = 51.84 dollars.
- Cost for a 3-month summer: 1.728 x 90 = 155.52 dollars.
Result: About 9.6 kWh and 1.73 dollars a day, near 51.84 dollars a month, or roughly 156 dollars across a three-month summer.
Typical appliance wattages and what each costs to run for one hour at 0.15 dollars per kWh
| Appliance | Typical power | Energy per hour | Cost per hour |
|---|---|---|---|
| LED bulb | 10 W | 0.010 kWh | $0.0015 |
| Laptop | 50 W | 0.050 kWh | $0.0075 |
| TV | 100 W | 0.100 kWh | $0.015 |
| Refrigerator (avg draw) | 150 W | 0.150 kWh | $0.023 |
| Microwave | 1000 W | 1.000 kWh | $0.150 |
| AC window unit | 1200 W | 1.200 kWh | $0.180 |
| Space heater | 1500 W | 1.500 kWh | $0.225 |
| Electric oven | 2400 W | 2.400 kWh | $0.360 |
How the same 1,500 W space heater cost changes with your rate (3 hours a day)
| Rate per kWh | Cost per day | Cost per month | Cost per year |
|---|---|---|---|
| $0.10 | $0.45 | $13.50 | $164.25 |
| $0.15 | $0.68 | $20.25 | $246.38 |
| $0.20 | $0.90 | $27.00 | $328.50 |
| $0.30 | $1.35 | $40.50 | $492.75 |
Estimated yearly cost of common appliances at typical daily use (0.15 dollars per kWh)
| Appliance | Power | Typical use | Energy per year | Cost per year |
|---|---|---|---|---|
| Phone charger | 5 W | 3 h/day | 5 kWh | $0.82 |
| LED bulb | 10 W | 5 h/day | 18 kWh | $2.74 |
| Ceiling fan | 60 W | 8 h/day | 175 kWh | $26.28 |
| Laptop | 50 W | 6 h/day | 110 kWh | $16.43 |
| LED TV | 100 W | 5 h/day | 183 kWh | $27.38 |
| Electric oven | 2400 W | 1 h/day | 876 kWh | $131.40 |
| Clothes dryer | 3000 W | 1 h/day | 1,095 kWh | $164.25 |
| Space heater | 1500 W | 3 h/day | 1,643 kWh | $246.38 |
| Window AC | 1200 W | 6 h/day | 2,628 kWh | $394.20 |
Find watts from the label when only amps and volts are given (Watts = Amps x Volts)
| Current | At 120 V (US outlet) | At 240 V (large appliance) |
|---|---|---|
| 1 A | 120 W | 240 W |
| 3 A | 360 W | 720 W |
| 5 A | 600 W | 1,200 W |
| 10 A | 1,200 W | 2,400 W |
| 15 A | 1,800 W | 3,600 W |
| 20 A | 2,400 W | 4,800 W |
Common mistakes to avoid
- Confusing watts with kilowatts. A 1,500 W heater is 1.5 kW, not 1,500 kW. You must divide watts by 1,000 before multiplying by hours and rate. Skipping that step overstates the cost by a factor of a thousand.
- Using hours plugged in instead of hours running. A fridge is connected all day but its compressor only runs part of the time, so its average draw is far below its peak. Use realistic running hours (or an average wattage) or your estimate will be much too high.
- Leaving out delivery charges in your rate. The supply price per kWh is only part of the bill. Delivery, distribution, and taxes are often just as large. Use the all-in rate (total bill divided by total kWh) for a realistic cost.
- Assuming the listed wattages match your exact appliance. The appliance list uses representative averages. Your model may draw more or less, and heaters and ACs cycle with a thermostat. For accuracy, read the nameplate watts or use a plug-in power meter.
- Judging an appliance by wattage alone. Cost is watts times hours, so hours matter as much as power. A 2,400 W oven used 20 minutes can cost less than a 60 W fan left on all day. Always compare on total kWh, not the wattage sticker.
- Ignoring standby (vampire) power. Devices that look "off" (TVs, consoles, chargers, smart speakers) often draw a few watts around the clock. Individually tiny, but summed over a year and many devices they add real dollars. Enter their idle watts at 24 hours to see it.
Glossary
- Watt (W)
- A unit of electrical power, the rate at which a device uses energy at a given moment. Higher watts means faster energy use.
- Kilowatt (kW)
- One thousand watts. Divide watts by 1,000 to get kilowatts.
- Kilowatt-hour (kWh)
- The amount of energy used by a 1,000-watt device running for one hour. This is the unit your electric bill charges for.
- Rate (price per kWh)
- How much your utility charges for one kilowatt-hour, in dollars. Use the all-in rate including delivery for accuracy.
- Nameplate rating
- The power in watts printed on an appliance label. It is usually the peak draw, which can be higher than the average running draw.
- Duty cycle
- The fraction of time a device actually draws power. A thermostat-controlled fridge or heater has a duty cycle well below 100 percent.
- Standby (vampire) power
- The small amount of electricity a device draws while switched off or idle, often 1 to 10 watts, running 24 hours a day.
- Time-of-use (TOU) rate
- A pricing plan where the price per kWh changes by hour of day, so the same appliance costs more at peak times than off-peak.
Frequently asked questions
How do I calculate the cost of running an appliance?
Divide the appliance power in watts by 1,000 to get kilowatts, multiply by the hours you use it per day to get kilowatt-hours, then multiply by your rate per kWh. For example, a 1,500 W heater used 3 hours a day at 0.15 per kWh is 1.5 x 3 x 0.15 = 0.68 dollars a day, or about 246 dollars a year.
What is a kWh and how does it relate to watts?
A kilowatt-hour (kWh) is the energy used by a 1,000-watt device running for one hour. To get kWh from watts, divide the watts by 1,000 (to get kilowatts) and multiply by the number of hours it runs.
What electricity rate should I use?
Use the all-in price per kWh from your bill, which means the total amount you paid divided by the total kWh used, including delivery and taxes. That is usually higher than the supply-only rate. The tool defaults to 0.15 dollars per kWh as a common example, while the U.S. residential average is roughly 16 to 17 cents.
Why does the monthly cost use 30 days and not the exact month length?
The monthly figure multiplies the daily cost by 30 for a clean, easy estimate. A true calendar-average month is 30.44 days, so real monthly costs are very slightly higher; the yearly figure uses the full 365 days.
How much does it cost to run a 1,500 watt heater?
At 0.15 dollars per kWh a 1,500 W heater costs about 0.225 dollars for each hour it runs. Running it 3 hours a day works out to roughly 0.68 dollars a day, 20.25 dollars a month, and 246 dollars a year.
Why is my fridge cheaper than its wattage suggests?
A refrigerator is plugged in all day but its compressor cycles on and off, so its average power draw is far below its peak rating. Use an average wattage (around 150 W or less for modern ENERGY STAR models) or the average running hours, not 24 hours at full power.
How do I find the wattage of my appliance?
Check the label or nameplate on the appliance or its power supply. If it lists amps and volts instead of watts, multiply them (watts = amps x volts), so a 5 A device on a 120 V outlet is about 600 W. For the most accurate figure, use a plug-in power meter that measures real usage.
Does leaving appliances on standby really cost money?
Yes, though a little. Devices on standby often draw 1 to 10 watts around the clock. A single 5 W idle load costs about 0.66 dollars a year at 0.15 per kWh, but a home with dozens of them can lose a noticeable amount, which is why switched power strips can pay off.
How can I lower my electricity cost?
Cut watts or cut hours, since cost is watts times hours. Switch to LED lighting and ENERGY STAR appliances to lower watts, and use timers, thermostat setbacks, and simply turning things off to lower hours. Focus first on high-wattage devices that run for long stretches, like heating, cooling, and water heating.
Is this electricity cost calculator accurate?
The math is exact for the numbers you enter. Accuracy depends on your inputs: use real running hours and your true all-in rate. Appliances with thermostats or variable loads will vary, so treat the result as a close estimate rather than an exact bill.
Is my data private?
Yes. All calculations run locally in your browser with JavaScript. Nothing you type is sent to a server, so your usage and rate stay on your own device.
Sources
- Electricity explained: Factors affecting electricity prices , U.S. Energy Information Administration (EIA)
- Estimating Appliance and Home Electronic Energy Use , U.S. Department of Energy