Enter an appliance's wattage, how many hours a day it runs, and your electricity rate to estimate its energy usage and cost daily, monthly and yearly.
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Energy usage in kilowatt-hours (kWh) is calculated as watts × hours used ÷ 1000, since a kilowatt-hour is 1000 watts sustained for one hour. That daily figure is then scaled up to monthly and yearly usage, and multiplied by your cost per kWh (found on your electricity bill) to estimate cost.
Check the appliance's nameplate, manual, or a label near the power cord, it's often listed directly in watts. If only amps and voltage are given, multiply them together (watts = amps × volts) to get an estimate.
A 1500W space heater run 3 hours a day at $0.15 per kWh: daily usage = 1500 × 3 ÷ 1000 = 4.5 kWh, costing 4.5 × $0.15 = $0.68 per day. Over a 30-day month that's 135 kWh costing $20.25, and annualized (using 365 days) it comes to 1,642.5 kWh, or roughly $246.38 per year, for one appliance run on that schedule.
Entering an appliance's amp rating in the watts field directly, if the nameplate only lists amps and voltage, multiply them together first (watts = amps × volts), plugging the amp figure straight into a watts field understates usage significantly for most household voltages.
Using full running wattage for an appliance that mostly cycles on and off, like a refrigerator or AC unit, these don't draw their rated wattage continuously, use an estimated average or effective daily run time instead of assuming full-power operation for the entire period.
Forgetting that daysPerMonth affects the monthly figure but the yearly figure is always calculated from a fixed 365 days times the daily rate, not by multiplying the monthly figure by 12, so a daysPerMonth value other than about 30.4 will make the monthly and yearly figures not scale by exactly 12x.
It's listed on your electricity bill, often called the 'energy charge' or 'supply rate', usually in cents or dollars per kWh.
Not directly, this calculator assumes the wattage you enter is drawn for the full duration you specify. For cycling appliances, use their average or effective run time per day for a more accurate estimate.
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