Energy Consumption Calculator
What a Device's Wattage Actually Costs You
An appliance's wattage rating is only half the story — a 1,500-watt space heater running for four hours a day costs vastly more than the same wattage rating suggests if you're only picturing an instant. Energy consumption is a function of power, time, and how many days it runs, which is exactly what turns a nameplate rating into a real electricity bill line item.
The Formula
Cost = Energy × Rate
Dividing by 1,000 converts watt-hours to kilowatt-hours, the unit utilities actually bill in. Multiplying that by the local electricity rate ($/kWh) turns raw energy use into a dollar figure.
Where This Calculation Is Useful
- Identifying energy hogs — running several household devices through the same formula quickly reveals which ones actually dominate a bill versus which just feel like they should.
- Justifying an upgrade — comparing the annual cost of an old appliance against a more efficient replacement's wattage makes the payback period concrete.
- Budgeting seasonal costs — a space heater or window AC unit run only part of the year benefits from a days-used input rather than a flat monthly assumption.
Common Household Devices
| Device | Daily use | kWh/month | Cost/month |
|---|---|---|---|
| LED bulb (10W) | 5 hours | 1.5 | $0.22 |
| Refrigerator (150W) | 24 hours | 108.0 | $16.20 |
| Laptop (65W) | 6 hours | 11.7 | $1.75 |
| Space heater (1,500W) | 4 hours | 180.0 | $27.00 |
| Window AC unit (1,000W) | 8 hours | 240.0 | $36.00 |
Wattage figures are typical ranges for each device category; actual wattage varies by specific model. Costs computed directly from the calculator's own formula at a $0.15/kWh example rate — substitute your own local rate for an accurate bill estimate.
How to Use This Calculator
- Enter the device's Power in Watts (check the nameplate or manual).
- Enter Hours Used per Day.
- Enter the Number of Days you want to estimate over.
- Enter your Electricity Rate in $/kWh.
- Select Calculate to get total energy used and its cost.
Related Calculations
Weigh that cost against going solar with the Solar Savings Calculator, or see the CO2 impact of that electricity use with the Carbon Footprint Calculator.