How to Calculate Monthly Electricity Cost for Any Appliance
Learn the kWh formula, run appliance examples, and understand why usage hours and local rates change monthly electric bills.
Last reviewed: July 5, 2026. This guide explains the real math behind an appliance electricity estimate and shows how to avoid the common mistake of blaming the wrong device for a high bill.
The formula in plain English
Electricity is billed in kilowatt-hours. Convert appliance watts into kilowatts, multiply by the hours used, then multiply by your electricity price.
Formula: watts ÷ 1,000 × hours per day × days × price per kWh = estimated cost.
Worked examples
| Appliance | Input | Monthly estimate |
|---|---|---|
| Space heater | 1,500 W × 4 h/day × 30 days × $0.17 | 180 kWh · $30.60 |
| Ceiling fan | 70 W × 8 h/day × 30 days × $0.17 | 16.8 kWh · $2.86 |
| Gaming PC setup | 450 W × 5 h/day × 30 days × $0.17 | 67.5 kWh · $11.48 |
The heater costs much more because heating loads are usually high wattage. Small devices can still matter if they run many hours, but heat, cooling, and compressors usually deserve the first check.
Numbers to verify before trusting the result
- Use the actual kWh rate from your bill, not a random average.
- For variable devices like refrigerators and AC units, use measured energy if you have a smart plug or manufacturer energy label.
- Separate weekday and weekend usage when your schedule changes.
- Remember that your final bill may include fixed fees, taxes, tiers, or minimum charges.
Common mistakes
- Typing 1.5 when the form expects 1,500 watts.
- Using the maximum wattage for a device that cycles on and off.
- Multiplying by 24 hours for a device that is actually on a timer.
- Comparing two appliances without using the same rate and usage hours.
Related calculator
Use the Electric Bill Calculator to test your own numbers after reading the guide.