What anything plugged in actually costs you
Electricity is sold by the kilowatt-hour (kWh) — one thousand watts running for one hour — but appliances are labelled in watts and used for hours, so the true cost of anything is never visible on the device itself. This calculator joins the three numbers up: enter an appliance's watts, how many hours a day it runs, and your electricity rate from your bill, and it returns the daily, monthly and yearly cost. At the defaults — a 100-watt television, 10 hours a day, at 15 cents a kWh — the answer is a tidy teaching example: exactly 1 kWh a day, 15 cents a day, $4.50 a month, $54.75 a year. The presets cost the usual suspects in one click, from a 10-watt LED bulb that runs for pennies to a 1,500-watt heater that quietly becomes one of the most expensive things in the house. It is the electrical sibling of the Fuel Cost Calculator: same idea, different tank.
The formula, and finding your three numbers
The watts are printed on a label on almost every device, on its power brick or in its manual; for motor-driven appliances like fridges, that label states a peak, while a fridge's compressor cycles on and off, so its honest average draw is lower — the 150-watt preset is an average, not the label figure. Hours per day is the number people guess worst: a television left on as background can double its honest hours, and a heater's season is three months, not twelve, which is why the yearly figure should be scaled to real use. The rate is the all-in figure on your bill — divide a bill's total by its kWh if the headline rate hides delivery and fees, because those extras are part of what an extra kWh costs you too.
Where the money actually goes
Running the presets side by side teaches the one lesson worth learning: cost follows the product of watts and hours, and heating and cooling dominate both. A space heater or air conditioner at 1,500 watts for 8 hours a day costs about $54 a month at 15 cents — more than a television, laptop, LED lighting for the whole house and the fridge combined, several times over. At the other end, the swap from a 60-watt incandescent bulb to a 10-watt LED saves about 0.05 kWh per hour of light: trivial per hour, roughly $27 a year for a bulb used ten hours a day, and the reason lighting upgrades pay back while most “energy-saving” gadgets do not. Big draws used briefly — a 1,000-watt microwave for ten minutes — cost about 2.5 cents a session; the bill is written by medium draws used constantly and large draws used for hours.
Worked example
Default example, worked in full: 100 W × 10 h = 1,000 Wh = 1 kWh per day. At $0.15 per kWh that is $0.15 a day, $4.50 per 30-day month and $54.75 a year (365 days). Change any of the three inputs and every figure rescales in proportion — double the hours or double the rate and the cost exactly doubles.
How to use this calculator
- Choose a preset appliance, or read the watts from your own device's label.
- Type the watts if you are costing something of your own.
- Enter honest hours per day — background hours count.
- Enter your electricity rate from your bill (total divided by kWh is the honest all-in rate).
- Read the monthly cost in the headline and the daily and yearly figures in the table.
Standby power: the small print of every bill
Devices with a plug and a clock, a remote sensor or a glowing dot draw power while “off” — typically 1 to 10 watts each, around the clock. One 5-watt standby load is 0.12 kWh a day, about $6.57 a year at the default rate: nothing, until a house's twenty such loads add up to a television's worth of yearly cost that bought no light, heat or entertainment at all. The calculator handles standby honestly — set the hours to 24 and the watts to the standby figure — and the fix it points to is unglamorous: power strips with switches for entertainment corners and chargers, where one click ends the whole group's quiet sipping. Measure before you moralise, though: a modern phone charger idling draws so little that unplugging it saves cents a year, while an old games console or a set-top box on standby can draw ten times a charger's figure.