Ever stared at a power bill and wondered which gadget is eating it? This calculator turns the mystery into a number. You give it three things about each appliance: how many watts it draws, how long it runs, and what you pay per kilowatt-hour. It hands back the daily, monthly, and yearly cost.
The real trick is doing several appliances at once. Add a row for the fridge, the AC, the gaming PC, that second freezer in the garage, and the tool sums them into one household total. Suddenly the bill stops being a single scary figure and becomes a list you can actually argue with.
How the math works
Every cost here rides on one tiny formula:
kWh = watts × hours ÷ 1000
That’s it. A 60W bulb left on for 10 hours uses 0.6 kWh. Multiply by your rate and you’ve got the cost. Want the monthly number? Multiply daily kWh by how many days you actually use the thing. The yearly figure just repeats that month twelve times.
Rate is the part people get wrong. Your “price per kWh” is printed on the bill, usually between $0.10 and $0.40 depending on where you live. The currency box is plain text, so swap the $ for €, £, ₺, or ₹ and the labels follow along.
A quick example
Say you run a 1500W space heater four hours a night, 25 nights a month.
- Daily: 1500 × 4 ÷ 1000 = 6 kWh
- At $0.17/kWh that’s about $1.02 a day
- Monthly: roughly $25.50
- Yearly (if you ran it like that all year): around $306
Now you can see why that one heater feels like it doubled the bill in winter. Compare it to a 9W LED bulb and the gap is almost comical.
Reading the totals
Four cards sit at the bottom: energy used per month in kWh, then cost per day, per month, and per year. The monthly cost card is the one most people fixate on, since bills arrive monthly. But honestly, the yearly number is more useful for big decisions. “$3 a month” sounds like nothing. “$36 a year, for ten years, is $360” is how you justify replacing an old fridge.
Each appliance row also shows its own monthly cost and kWh, so you can spot the hog instantly. Sort it out in your head: the things that run 24/7 (fridge, router, standby electronics) often beat the things that feel power-hungry but only run briefly.
Good to know
These numbers are estimates, and they’re honest ones, but they’re not your exact bill. Real utilities tack on a fixed supply or connection charge every month no matter what you use. Many also use tiered pricing (the more you use, the higher the per-kWh rate climbs) or time-of-use rates where 6pm electricity costs triple the 2am price. None of that shows up here.
Nothing you type leaves your browser. There’s no server, no upload, no log. Punch in numbers, read the result, close the tab. The math runs locally the instant you change anything.
Common questions
Where do I find the watts for an appliance? Check the label on the back or bottom, or the manual. It’s listed as W or sometimes as volts and amps (multiply those two to get watts). For motors and heaters the rated wattage is close enough.
My device shows amps, not watts. Now what? Multiply amps by your voltage. In North America that’s roughly 120V, so a 10A appliance pulls about 1200W. Most of Europe and Asia run 220 to 240V.
Why is the yearly number so much higher than I expected? Small daily costs compound. A device sipping $0.10 a day still costs $36.50 over a year. Run a few of those and it adds up fast.
Does standby power count? Yep, and it’s sneakier than you’d think. A TV or console pulling 5W in standby for 20 idle hours a day still racks up kWh. Add a row for it and watch.
Can I use this outside the US? Sure. Set the currency box to your symbol and the rate to your local price per kWh. The formula is the same everywhere on the planet.