Home / Solar Draft Tools / Solar Size Calculator — How Many Solar Panels Do You Need?
Free Solar Draft Tool
Solar Size Calculator
Enter your monthly electricity bill and Solar Draft estimates the system size, panel count and roof area you'll need.
Enter your details
Check a recent bill — most Indian DISCOMs charge ₹6–₹10/unit.
4–5 hrs for most of India; use 5.5 for Rajasthan/Gujarat.
Recommended System Size
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Panels needed—
Roof area needed—
Est. monthly units consumed—
Est. monthly generation—
DisclaimerEstimates only, using standard industry rules of thumb (100 sq. ft. per kW, 80% performance ratio). Actual system size depends on your roof's real shading, orientation and available area — get a free 3D design from Solar Draft for exact numbers.
How this Solar Draft calculator works
Solar system sizing comes down to matching how much electricity you use to how much a rooftop system can realistically generate in your city.
- Your monthly units consumed are estimated from your bill and tariff rate.
- Your system size (kW) is sized so daily generation covers your average daily usage, accounting for an 80% performance ratio (inverter losses, wiring, dust).
- Panel count and roof area follow from the system size and your chosen panel wattage.
This is a quick estimate for planning purposes. Actual sizing should always account for real roof shading, orientation and available space — see how many solar panels you actually need on the Solar Draft blog for the full picture.
Want the exact numbers for your roof?
Solar Draft's 3D design tool gives you real panel count, real shading and a ready proposal.