Why use an electricity cost calculator?

For appliances like air conditioners, heaters, dehumidifiers, gaming PCs, or home servers, it is often hard to guess the real running cost.

This tool helps you estimate cost using just four inputs:

  • Power consumption (W)
  • Hours used per day
  • Days used per month
  • Electricity price per kWh

What was improved in this quality pass

This calculator previously accepted zero, negative, more than 24 hours per day, more than 31 days per month, and fractional usage days without a clear error. Its prefilled result also hid the empty state. Because an appliance estimate can be mistaken for a real utility bill, this update prioritizes input validation, a clear empty state, and explicit calculation assumptions.

Accepted ranges are 0.1–1,000,000 W, 0.1–24 hours per day, 1–31 whole usage days, and 0.01–1,000,000 per kWh. Out-of-range entries now show a specific error instead of a misleading result.

How to use the calculator

  1. Enter the appliance’s rated power in watts (W).
  2. Enter how many hours it runs per day.
  3. Enter the number of days it runs in a typical month.
  4. Enter your electricity price per kWh.
  5. Review daily and monthly usage plus the estimated daily, monthly, and yearly cost.

The result stays blank until all four inputs are valid. Use Fill sample to load a 1500 W heater example, Copy result to copy a valid summary, or Clear to return to the empty state.

How it works

The calculation is straightforward:

  1. Watts ÷ 1000 = kW
  2. kW × hours per day = daily usage (kWh)
  3. Daily usage × number of days = monthly usage (kWh)
  4. Monthly usage × electricity price = estimated monthly cost

It also shows daily cost, monthly cost, and yearly cost, which makes it useful when comparing appliances.

Example

Electric heater

  • Power: 1500W
  • Usage: 4 hours/day
  • Days: 30
  • Electricity price: 150 KRW/kWh

→ Daily usage: 6kWh
→ Monthly usage: 180kWh
→ Estimated monthly cost: 27,000 KRW

Dehumidifier

  • Power: 300W
  • Usage: 8 hours/day
  • Days: 20
  • Electricity price: 150 KRW/kWh

→ Monthly usage: 48kWh

→ Estimated monthly cost: 7,200 KRW

Good use cases

  • Estimate air conditioner or heating cost
  • Calculate home lab / server electricity usage
  • Compare the operating cost of multiple appliances
  • Check whether a device is worth running every day

Empty and error states

  • Blank input: no cost is shown until all four fields are complete.
  • Wattage: enter 0.1–1,000,000 W.
  • Daily use: enter 0.1–24 hours.
  • Monthly use: enter a whole number from 1 to 31 days.
  • Electricity price: enter 0.01–1,000,000 per kWh.

The calculator does not silently clamp an invalid value. Correct the highlighted field before copying a result.

FAQ

Why is the estimate different from my actual bill?

Real electricity bills often include more than just energy usage, such as base fees, taxes, and progressive pricing. Use this tool as a quick estimate for a single appliance or usage pattern.

The yearly estimate assumes the entered monthly pattern repeats for 12 months. Calculate seasonal usage separately when operating hours change during the year.

What is the difference between W and kW?

1000W equals 1kW. If your appliance label says 800W or 1500W, divide by 1000 to convert it into kW.

Can I use this to compare appliances?

Yes. Enter each appliance one by one and compare the monthly cost to see which one uses more electricity.

Summary

This electricity cost calculator turns appliance wattage and operating time into kWh usage and a quick cost estimate. Use it to compare devices, then check your utility’s rate structure when you need a bill-level estimate.