“Just unplug it, it’s costing you money” is common advice — but how much, really? Our electricity cost calculator turns wattage and usage hours into an actual dollar figure.
The math
kWh per day = (Watts × Hours per day) ÷ 1,000
Daily cost = kWh per day × your rate ($/kWh)
Monthly cost = Daily cost × 30
Yearly cost = Daily cost × 365Electricity is billed in kilowatt-hours, not watts, which is why the wattage gets divided by 1,000 before multiplying by your rate.
Finding your inputs
- Wattage: check the appliance’s nameplate, spec sheet, or manual. If it only lists amps and volts, multiply them together to get watts. A plug-in power meter gives the most accurate real-world reading for appliances with variable draw.
- Rate: check your latest electricity bill for the per-kWh “energy charge.” Rates vary a lot by region and utility, and some plans have tiered or time-of-use pricing this simple calculator doesn’t model.
Example
A 1,500W space heater running 3 hours a day at $0.15/kWh: about $0.68/day, $20.25/month, and roughly $246/year — a useful sanity check before deciding whether that heater (or old fridge, or gaming PC) is worth the running cost.
One thing it doesn’t include
Standby “vampire” power draw — many electronics pull a small amount of power even when switched off but still plugged in. This calculator only covers active-use hours; measure standby wattage separately and add it as its own 24-hour entry for a fully accurate picture.