Solar Panel Calculator — Free Online Calculator
Calculate how many solar panels you need based on your electricity usage, location, and panel wattage. Free solar sizing tool with cost estimates.
How to Use This Calculator
Enter your average monthly electricity usage in kWh (from your utility bill), select your area's peak sun hours, choose a panel wattage, and how much of your usage you want to offset. The calculator determines how many panels you need and estimates system cost.
The Formula Explained
Solar system sizing starts with your daily energy need: Daily kWh = Monthly kWh / 30. The system size accounts for production losses (~20%): System kW = Daily kWh / (Sun Hours × 0.8). Number of panels = System kW × 1000 / Panel Watts. Cost estimates use $2.50–$3.50 per watt installed (national average before the 30% federal tax credit).
Solar System Size by Monthly Usage (5 Peak Sun Hours, 400W Panels)
| Monthly kWh | Panels | System Size | Est. Cost |
|---|---|---|---|
| 500 kWh | 6 | 2.4 kW | $6,000–$8,400 |
| 750 kWh | 8 | 3.2 kW | $8,000–$11,200 |
| 1000 kWh | 11 | 4.4 kW | $11,000–$15,400 |
| 1500 kWh | 16 | 6.4 kW | $16,000–$22,400 |
| 2000 kWh | 21 | 8.4 kW | $21,000–$29,400 |