Ecology & Environment

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Solar Panel Wattage Calculator.

Calculate electrical power from panel voltage and current using P = V × I.

On-device calculationNo signup
01

Set your values

Results update as you type.

Power: 400 W

Power

400.000000W
Power: 0.4 kW

Power

0.400000kW

Results update automatically as you type.

Use Cases

Sizing a solar panel system

Determine the total wattage of panels needed to meet your daily energy consumption by calculating each panel's output.

Example: If you need 3 kW and each panel is 300W, you'll need 10 panels.

Comparing solar panel performance

Evaluate different panels by their wattage to choose the most efficient option for your space and budget.

Example: Compare a 250W panel vs a 300W panel for the same roof area.

Frequently Asked Questions

How do I calculate solar panel wattage?
Multiply the panel's voltage (V) by its current (A). For example, a panel with 18V and 5.5A produces 99W. This calculator does that for you instantly.
What units are used in this calculator?
Voltage is entered in volts (V) and current in amperes (A). The result is the electrical power in watts (W).
Why is knowing solar panel wattage important?
It helps you estimate energy production, size your solar system, and compare panels. For instance, a 300W panel produces about 1.5 kWh per day in good sunlight.

Tips & Common Mistakes

Tips

  • Check the voltage and current ratings on your solar panel's label or datasheet for accurate results.
  • Use the actual operating voltage and current, not just open-circuit voltage, for real-world wattage.
  • Consider that solar panels produce less than rated wattage in real conditions due to temperature and shading.
  • Multiply the wattage by peak sun hours to estimate daily energy production.

Common Mistakes to Avoid

  • Using open-circuit voltage (Voc) instead of maximum power voltage (Vmp) leads to overestimated wattage.
  • Forgetting to convert units if your panel's current is given in milliamps (mA) – divide by 1000 to get amps.
  • Assuming the calculated wattage is the actual output under all conditions; real output varies.

Last updated: August 13, 2026