π Appliance Wattage Calculator
Monthly kWh, cost, and yearly spend for any appliance.
Estimated monthly cost
How to Use This Calculator
Enter the appliance's wattage from its label, how many hours a day it actually runs, your electricity rate in cents per kWh, and days per month. The calculator returns the monthly cost as the headline, with monthly kWh, daily cost, and yearly cost in the details. The default rate of 18 cents matches the recent US residential average, but your bill is the truth: Hawaii households pay more than triple Louisiana's rate, so the same space heater costs three times as much to run. Always use your own rate for decisions that involve money.
Find the wattage on the appliance label, manual, or spec sheet. Amps x volts = watts if only those are listed.
Estimate honest daily hours. A fridge "runs" 24 hours but its compressor cycles, so use 8 to 12 equivalent full-power hours.
Enter your rate from your electric bill. The US average sits near 18 cents per kWh, with wide state variation.
Hit Calculate Cost and compare the yearly figure against the price of a more efficient replacement.
The Method: Watts to Dollars
Energy is power times time, and the kilowatt-hour is the billing unit that packages both. Divide watts by 1,000 to get kilowatts, multiply by hours to get kWh, multiply by your rate to get dollars. The worked example shows a space heater at 4 hours a day costing $32.40 a month at 18 cents per kWh, or $388.80 a year. That yearly number is the one that should drive purchase decisions: a $60 efficient alternative that cuts the draw in half pays for itself in under two months of heavy use. The subtlety is duty cycle: labels show maximum draw, but thermostats and compressors cycle, so a 1,500-watt heater with a thermostat might average 900 watts over an evening. When in doubt, a $25 plug-in power meter gives you the true number for a week.
Worked Example
A window AC unit rated 1,200 watts runs 8 hours a day through a 30-day month at 18 cents per kWh. Monthly kWh = 1,200 x 8 x 30 / 1,000 = 288 kWh. Monthly cost = 288 x 0.18 = $51.84. Yearly, if it runs four months, that is $207.36. Now compare a newer 900-watt unit with the same cooling output: 900 x 8 x 30 / 1,000 = 216 kWh, costing $38.88 a month, saving $12.96 monthly or $51.84 per cooling season. If the efficient unit costs $80 more, payback arrives in under two seasons. This is the entire logic of energy-efficient appliances compressed into one comparison.
Typical Wattages for Common Appliances
Space heater 1,500; hair dryer 1,200 to 1,875; microwave 1,000 to 1,200; toaster oven 1,200; coffee maker 800 to 1,200; window AC 900 to 1,400; clothes dryer 3,000 to 5,000 (usually 240-volt); electric range burner 1,500 to 2,500; refrigerator 100 to 400 while running; chest freezer 100 to 300; LED bulb 8 to 12; old incandescent bulb 60; TV (LED, 55 inch) 60 to 150; gaming console 150 to 350 under load; desktop computer 200 to 500; laptop 30 to 90; phone charger 5 to 20. Two patterns jump out: anything that makes heat or cold is expensive, and anything with a screen or chip is cheap. When hunting bill savings, start with the heaters.
Cutting the Bill Without Sacrifice
The biggest wins are behavioral, not purchases. Lowering the water heater from 140 to 120 degrees saves real money with zero lifestyle change. Washing clothes cold and line-drying when practical attacks the dryer's 3,000-plus watts. Sealing the worst air leaks does more than a fancy thermostat. LED swaps pay back in months because the old bulbs were little heaters that happened to glow. Smart power strips kill standby loads you will never miss. Run each candidate change through the calculator with before-and-after wattages: seeing "$96 a year" next to a habit change is what actually sustains it past February.
Generator Sizing for Outages
Generator shopping is applied wattage math: list everything you must run, sum the running watts, then add the largest starting surge. A fridge (150 running, 1,200 starting), a few lights (60), phone chargers (30), and the furnace blower (500 running, 1,000 starting) total under 1,000 running watts but need ~2,500 of surge capacity. Portable generators are rated in running watts with a higher surge rating; size to the surge. Inverter generators cost more but run quieter and produce cleaner power for electronics. Never backfeed through a dryer outlet; use a transfer switch installed by an electrician. And run the generator 20+ feet from the house: carbon monoxide kills more people in outages than the outage itself.
A Second Worked Example: The Old Fridge
A 1990s refrigerator averaging 150 watts over 10 equivalent full-power hours a day. Monthly kWh: 150 times 10 times 30 divided by 1,000 is 45 kWh. At 18 cents: $8.10 a month, $97.20 a year. A modern efficient fridge might use half that, saving around $50 a year. Against a $1,000 replacement, the payback is 20 years on energy alone, which is why old fridges in garages keep running: the math rarely justifies replacing a working fridge for efficiency.
The exception is the truly ancient unit: pre-1990 fridges can draw triple the modern figure, and at that point the power bill starts rivaling a payment. Run your actual numbers; the calculator exists because the answer varies by unit, rate, and duty cycle.
Vampire Loads: The Standby Tax
Devices draw power when "off": TVs, cable boxes, game consoles, chargers, anything with a remote or a clock. Individually it is watts; across a house it is estimated at 5 to 10 percent of residential electricity. A house with a $150 monthly bill may feed $10 to $15 a month to devices doing nothing.
The fixes are cheap: power strips that switch off the entertainment center, unplugging chargers, and enabling real sleep modes on consoles and computers. Measure with a plug-in meter for the honest numbers; the worst offenders are usually the cable box and the old game console, not the phone charger. Kill the standby tax and the bill drops with zero lifestyle change.
Common Wattage Mistakes
First: label max versus duty cycle. A 1,500-watt heater with a thermostat averages far less; a fridge "running" 24 hours compresses 8 to 12. Use equivalent full-power hours, not plug-in hours. Second: the wrong rate. The 18-cent default is a national average; your bill's actual rate, including delivery charges, is the truth.
Third: forgetting the rate structure. Time-of-use plans charge more at peak; running the dryer at 6 PM can cost double the midnight rate. Fourth: the generator fallacy. Sizing a generator from running watts alone ignores startup surge, which can triple the draw on motors; size for surge. Fifth: the efficient-replacement reflex. A $60 gadget that saves $2 a month takes 30 months to pay back; run the payback before buying the virtue.
Frequently Asked Questions
How do I find an appliance's wattage?
Check the label on the back or bottom of the appliance, the owner's manual, or the manufacturer's spec page. US appliances list watts directly; if you only see amps and volts, multiply them: watts = amps x volts. A standard 120-volt outlet with a 12-amp space heater means 1,440 watts. Enter the watts above with your daily use hours.
What uses the most electricity in a home?
Heating and cooling top the list, followed by the water heater, then the clothes dryer and electric range. Among plug-in appliances, space heaters (1,500 watts) and older refrigerators are the big ones. Small electronics like phone chargers and LED bulbs barely register. This calculator ranks any appliance you enter by monthly cost so the surprises become obvious.
How much does it cost to run a 1500-watt space heater?
At 18 cents per kWh, a 1,500-watt heater costs 27 cents per hour. Run 8 hours a day for a month and that is about $64.80. Space heaters are the classic bill shock: they feel small but draw as much as 25 LED bulbs. Enter 1500 watts and 8 hours above to see your own rate's version.
What is the formula for appliance energy cost?
Monthly kWh = watts x hours per day x 30 / 1,000. Monthly cost = monthly kWh x your electricity rate. A 100-watt bulb on 5 hours a day uses 15 kWh a month, which costs $2.70 at 18 cents per kWh. The calculator runs both steps and annualizes the result.
Do appliances use power when turned off?
Many do, called phantom or standby load. TVs, game consoles, cable boxes, and chargers can draw 1 to 10 watts around the clock. Ten watts of standby is 7.2 kWh a month, about $1.30. It is small per device but real across a house. A power strip you switch off kills the whole category at once.
How accurate is the estimated cost?
It is as accurate as your two inputs: the wattage and the hours used. Wattage on the label is usually the maximum draw, so cycling appliances like refrigerators and heaters use less in practice. Your electricity rate is the other lever: the US average is around 18 cents per kWh, but Hawaii pays over 39 cents and Louisiana around 12. Use your bill's rate for a true number.
Should I replace an old refrigerator to save energy?
Maybe. A 1990s fridge can use 1,000+ kWh a year while a modern Energy Star model uses under 500. At 18 cents per kWh that is $90+ a year in savings, so payback takes many years on a $1,200 fridge bought for energy reasons alone. Run both models through the calculator with realistic daily-equivalent hours before deciding.
What is a kilowatt-hour in plain terms?
It is 1,000 watts running for one hour. A 100-watt bulb burning for 10 hours uses one kilowatt-hour. Your electric meter counts these units, and your bill multiplies them by your rate. Everything electrical can be translated into kWh, which is why it is the universal currency of energy math.