Last updated October 13, 2026 · Report an error
Appliance power ratings are listed in watts, but electricity bills are priced per kilowatt-hour — converting between the two is the key to estimating what any device actually costs to run.
This calculator finds the energy used and total cost for any appliance based on its wattage and usage pattern.
How it works
Enter the appliance's power rating in watts, how many hours per day it runs, over how many days, and your electricity rate per kWh. The calculator converts watts to kilowatts, multiplies by total hours, then applies your rate.
- Enter appliance power (watts).
- Enter hours used per day.
- Enter number of days.
- Enter cost per kWh ($).
- Click Calculate to see your results.
Examples
1500W space heater, 3 hrs/day, 30 days
A 1500-watt space heater run 3 hours a day for 30 days uses 135 kWh, costing $20.25 at a $0.15/kWh rate.
Who should use it
- Estimating the running cost of a space heater, air conditioner, or other high-wattage appliance.
- Comparing the cost of leaving a device on longer versus using it more efficiently.
Industry applications
- Home energy management and budgeting
- Appliance and electronics retail (cost-of-ownership comparisons)
Advantages
- Simple conversion from watts and usage time directly to a dollar cost.
- Shows both total cost and a daily cost breakdown.
Limitations
- Assumes a flat electricity rate — doesn't model tiered or time-of-use pricing.
Common mistakes to avoid
- Confusing an appliance's wattage with its amperage or voltage rating.
- Using an outdated electricity rate that doesn't reflect your current bill.
Best practices
- Check your most recent electricity bill for your actual current rate per kWh rather than guessing.
Tips
- High-wattage appliances like space heaters, hair dryers, and electric water heaters are usually the biggest opportunities for cutting an electricity bill — check their cost here before assuming a small device is the culprit.
Frequently asked questions
Yes, with no signup and no limit on how many appliances you check.
Check the appliance's label, spec sheet, or manual — it's usually listed in watts (W) directly, or as amps and volts (watts = amps × volts).
Check a recent electricity bill — most utilities show your rate per kWh directly, though tiered or time-of-use rates may vary by usage level or time of day.
No — this calculator uses a single flat rate; for tiered or time-of-use billing, run the calculation separately for usage in each rate tier or time period.