A monthly electricity bill is a single total — the sum of every device running in your home, averaged over 30 days. It can't tell you, on its own, whether that old space heater or that always-on mini fridge is the thing actually driving the number up.
Electricity cost calculator, per device
Enter a device's wattage (found on the device itself, its power adapter, or its spec sheet), how many hours a day you run it, and how many days — this isolates that one device's cost from everything else on the bill.
kWh cost calculator, using your actual rate
Enter your utility's per-kWh rate (from your bill) rather than a national average — rates vary significantly by location and time of use, and the math only means something with your real number plugged in.
Appliance running cost calculator, total and per day
See the total cost over the period you entered, the raw kWh used, and the cost broken down per day — useful for comparing two appliances or deciding whether a fix (a new fridge, a programmable thermostat) pays for itself.
