Daily Energy Use Calculator
Add the devices you use in a day to estimate watt-hours, kilowatt-hours, and a rough 30-day electricity cost. It is a handy starting number for a battery or solar plan.
Enter Your Devices
Use running watts and the average hours each device is on per day. The sample values below are just an example; replace them with your own labels or measurements.
Up to 10 devices. For a device that cycles on and off, use its estimated average draw or measure its actual daily energy.
$0.15 is an example, not a local rate. Enter your own rate, or leave it blank to skip cost.
Your Results
Daily energy
Daily kWh
30-day energy
30-day energy cost
By device
| Device | Wh/day |
|---|
Enter your values and calculate. These numbers estimate energy use, not the peak power or startup surge your inverter needs.
How to Use This Calculator
List each device, its running wattage, how many you use, and how many hours it operates in a typical day. The tool adds their daily energy use. For a battery or solar project, the Wh/day result is the useful starting point; it does not include system losses yet. Use a realistic average day, then consider a heavier-use day separately if you need a more conservative plan.
Look at the device label or manual for watts. If a label gives amps and volts instead, our watts to amps calculator can help with a conversion, but the actual draw may vary by operating mode. A plug-in energy meter is more useful for appliances that cycle or change speed.
How the Math Works
For each row, daily watt-hours = running watts × quantity × hours per day. Add the rows, then divide by 1,000 for daily kilowatt-hours. Multiply daily kWh by 30 for a 30-day estimate. If you entered an electricity rate, multiply those 30-day kWh by the rate for an energy-only cost estimate.
Example: Lights, a Laptop, and a Fan
Four 10W LED lights on for 5 hours use 200Wh per day. A 60W laptop used for 4 hours adds 240Wh, and a 35W fan for 8 hours adds 280Wh. Together that is 720Wh per day, or 0.72kWh per day. At the same use every day, 30 days comes to 21.6kWh. At an example rate of $0.15/kWh, the energy portion of the bill would be $3.24. Your equipment and rate will differ.
What the Estimate Leaves Out
- Labels may show rated or maximum watts rather than the average in use. A fridge, pump, or power tool will not necessarily draw the same watts all day.
- The cost figure excludes fixed charges, taxes, tiered rates, and time-of-use pricing. Read the relevant rate on your bill for a better estimate.
- This is energy consumed by the listed devices. Battery, inverter, wiring, and solar charging losses are separate inputs in the sizing tools.
- Daily energy does not tell you the simultaneous running watts or startup surge. Those matter when choosing an inverter.
Use the Daily Total in Your Next Step
Take the Wh/day number to the battery bank size calculator to plan storage over one or more days, or to the solar panel size calculator to estimate generation. If you know the battery you already have, the battery runtime calculator answers a different question: how long a steady load might run. For AC loads, check simultaneous running watts and surge with the inverter size calculator. Browse the full DIY calculators directory for related planning tools.
Source and Planning Note
The wattage and time method follows Virginia Cooperative Extension’s appliance energy worksheet. Check your actual device readings and manufacturer specifications. Use this page for an early estimate, not a final electrical design or a promise about your utility bill.