Solar

Solar System Size Calculator

By HowMuchWatts Editorial Team Reviewed June 30, 2026 Formula and source method

Before pricing solar, you need to know what size system covers your usage. This calculator estimates the kW and number of panels you need from your monthly electricity use.

Change any number below — your result updates instantly, no button to click.

Your details

Results

Recommended system size

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Approx. number of panels

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Daily energy to cover

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Optional next step

Measure or improve the real-world result

These tools are relevant to the numbers above; you do not need them to use the calculator.

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Portable solar panel kitA good entry point for offsetting daytime usage or off-grid setups.See options Solar power meterMeasure real sunlight at your site before sizing a system.See options

Written & maintained by the HowMuchWatts team · Last updated June 30, 2026 · How we verify our numbers

How it works

Daily use = monthly use × 12 ÷ 365. System size = daily use ÷ (peak sun hours × performance ratio ÷ 100). Panels = system size ÷ panel wattage. This sizes a system to roughly offset your annual use; exact sizing also depends on roof space, shading and net-metering rules.

Frequently asked questions

What are peak sun hours?

The number of hours per day where sunlight averages 1,000 W/m². It is less than daylight hours and varies by location and season.

Should I size for 100% of my usage?

Often yes, but if your utility pays little for exported power, sizing closer to your daytime usage can give a better return. Our solar payback calculator helps compare.

How much roof space do I need?

Roughly 1.7–2 m² (about 18–22 sq ft) per panel. Multiply by the panel count above to estimate the area.

These calculators provide general estimates for educational purposes only and are not financial advice. Real-world results depend on factors not captured here. Verify figures independently before making any purchase or financial decision.

Complete topic guide Solar Panel Costs & Savings Work through solar sizing, installed cost, savings, export income, payback, and battery value with transparent calculators and decision guidance.

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