Electricity Cost Calculator

Using the Electricity Cost Calculator

Work out what any appliance actually costs to run. The tool converts watts, hours, and days into daily, monthly, and yearly dollar figures using the rate you enter from your bill.

1. Power consumption (watts) - from the appliance nameplate. LED bulb 9 W, desktop PC 200 W, window AC 900 W, central AC 3,500 W, electric dryer 3,000 W, refrigerator 150 W running.
2. Hours per day - how long the device actually runs, not how long it is plugged in. A fridge runs its compressor about 8 hours per 24.
3. Days - 30 for monthly, 365 for yearly.
4. Electricity rate - your cost per kWh from the bill's "Energy Charge" or "Supply" line. US average is around $0.16/kWh as of 2024.
5. Read and copy - click any cost card to copy the formatted result.

The Formula and Why It Works

Core equation: kWh = Watts × Hours / 1000, then Cost = kWh × Rate. A 1,500 W space heater running 8 hours/day consumes 12 kWh daily. At $0.16/kWh, that is $1.92/day, $57.60/month, $700.80/year - often surprising the first time. The math runs on JavaScript IEEE 754 floats, accurate well past the cent for any realistic input. The formula assumes constant load; real appliances cycle, so enter duty-cycle hours, not plug-in hours.

Standby Power (Vampire Draw)

Many electronics draw 0.5-10 W when "off" - TVs, consoles in instant-on mode, cable boxes, smart speakers, printer power bricks. A 5 W continuous draw at $0.16/kWh costs $7/year. Across a dozen devices, standby can account for 5-10% of a typical US household bill (LBNL and DOE studies). Enter standby wattage at 24 hours/day to estimate.

Real Moments This Calculator Earns Its Place

• Deciding whether to leave a window AC on all day or only when you are home.
• Comparing LED vs. incandescent bulb running cost over a year.
• Costing a GPU workstation or mining rig for a home office.
• Calculating EV home charger cost (7.2 kW × 4 hours/day = 29 kWh daily, about $4.60/day in most US states).
• Evaluating whether a second garage fridge is worth the annual $80-150.

Regional Rate Variation and Time-of-Use

US residential rates span $0.10/kWh (Pacific Northwest hydro, Louisiana) to $0.43 (Hawaii). European rates average EUR 0.28/kWh across the EU, spiking past EUR 0.40 in Germany and Denmark. Australia averages AUD 0.33. Japan is around JPY 31. The calculator takes a single flat rate, which fits most US residential tariffs, but time-of-use plans charge different rates for peak and off-peak - a California summer TOU plan may bill $0.45/kWh from 4-9 pm and $0.28 otherwise. For TOU, run the calculator twice with the appropriate hour splits.

Edge Cases and Appliance Gotchas

Motor-driven appliances (fridges, AC compressors, vacuums) have a startup surge at 2-3x running wattage, but it lasts under a second - not a running-cost factor. Heating appliances convert nearly all wattage to heat, so nameplate wattage equals real consumption. Inverter mini-split heat pumps cheat: they move heat rather than generate it, delivering 3-4 kWh of heating per kWh consumed (COP 3-4). Electric vehicles charge at a stated rate but lose 10-15% to charging inefficiency. Solar households with net metering see their billed rate change direction during sunny hours.

How This Compares to Alternatives

A Kill-A-Watt plug-in meter or a smart plug with energy monitoring (TP-Link Kasa, Emporia) measures real-world wattage directly - more accurate than any calculator because it captures actual duty cycle. Whole-home monitors (Sense, Emporia Vue) clamp onto your breaker panel and track every circuit. Utility companies publish appliance-cost calculators tuned to their specific rate. This tool is fastest for a rough estimate when you know wattage and run time - no purchase, no app install. It will never match a physical meter because it cannot measure what your appliance actually draws.