Home & Electrical

Solar Panel Calculator: What Size Rooftop Solar Do I Need?

Free tool · Updated October 2, 2026 · By CouponTalk

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Quick answer

In most of India, 1 kW of rooftop solar produces about 4 units (kWh) a day, or 120 units a month. Divide your monthly units by 120 to get the system size: a home using 300 units a month needs about a 2.5 kW system, around 5 panels of 540 W and roughly 225–250 sq ft of shade-free roof.

How to use this calculator

Find your average monthly units on your electricity bill (average the last 12 months if you can).
Choose the panel wattage your installer quotes.
Enter the installed cost per kW from quotes and your tariff per unit.

Reference table

Rooftop solar size by monthly units (about 4 units per kW per day)
Monthly use	System size	540 W panels	Roof area
100 units	1 kW	2	90 sq ft
150 units	1.5 kW	3	135 sq ft
200 units	2 kW	4	180 sq ft
300 units	2.5 kW	5	225 sq ft
400 units	3.5 kW	7	315 sq ft
500 units	4.5 kW	9	405 sq ft
600 units	5 kW	10	450 sq ft

These are typical figures for Indian homes. Check the product spec sheet, and ask an electrician or installer before you buy or fit anything.

Frequently asked questions

How many solar panels do I need for my home?

Divide your monthly units by 120 to get kW, then divide by the panel wattage in kW. For 300 units a month: 300 ÷ 120 = 2.5 kW, and 2.5 kW ÷ 0.54 kW ≈ 5 panels of 540 W.

How much subsidy is available for rooftop solar?

Under the PM Surya Ghar Muft Bijli Yojana for homes, the central subsidy has been ₹30,000 per kW for the first 2 kW and ₹18,000 for the third kW, up to ₹78,000. Check pmsuryaghar.gov.in for current rules.

How much roof space does 1 kW of solar need?

About 80–100 sq ft of shade-free roof per kW with modern 540 W panels.