Battery & energy
Energy Usage Calculator
Household energy use equals the sum of each appliance's watts, daily runtime, and quantity. Period cost multiplies the resulting kilowatt-hours by your entered rate.
Add multiple appliances to estimate daily and period energy use plus cost at your entered electricity rate.
Calculated result
Aggregated energy use
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
Adjust each line to measured or documented average power and realistic runtime for your household.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Daily kWh = sum(watts x hours per day x quantity) / 1000; period cost = daily kWh x days x rate.
- W
- Average real power in watts.
- h
- Operating or charging time in hours.
- kWh
- Accumulated electrical energy in kilowatt-hours.
- rate
- User-entered electricity price per kilowatt-hour.
- η
- User-entered efficiency expressed as a decimal or percentage.
Each line supplies appliance name, average watts, daily hours, and quantity; rate is your entered price per kWh.
Worked example
| Input | Value |
|---|---|
| Appliances | See the example load list in the calculator |
| Number of days | 30 days |
The default refrigerator, lights, and television assumptions total 2.08 kWh per day, or 62.4 kWh over 30 days.
Reference table
| Appliance | Planning watts | Use note |
|---|---|---|
| LED lamp | 10 W | Nominal example |
| Laptop computer | 60–120 W | Typical planning range |
| Refrigerator while running | 100–250 W | Cycling load; startup can be higher |
| Microwave oven | 900–1,500 W | Input varies by model |
| Portable space heater | 1,500 W | Common high setting |
| Electric kettle | 1,200–1,800 W | Varies by market and model |
Frequently asked questions
How are multiple loads combined?
Each line's watts, hours, quantity, and days are converted to energy and then summed.
What format should each load use?
Enter one load per line using the labels and numeric fields shown in the input help text.
Can I enter several appliances?
Yes. Enter one appliance per line with its name, watts, hours per day, and quantity.
Assumptions and limitations
- No automatic appliance detection, rate database, seasonal profile, standby estimate, or demand charge.
- Constant average power is assumed for each line.
Method and sources
Review the electrical formulas, calculation methodology, and standards status for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .