Calculator

Solar System Size Calculator

Tell us your monthly bill or units. We work out the kW you need, how many panels that is, how much roof space it takes and how many units it will make.

Your consumption

From your electricity bill
Sets sun hours and metering rules
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The formula

Daily units = Monthly units / 30 System size (kW) = Daily units / (Sun hours x 0.75) 0.75 covers losses from the inverter, heat, dust and wiring. SUN HOURS BY REGION Rajasthan, Gujarat, Ladakh 5.5 MP, Maharashtra, Telangana, AP 5.0 Delhi, UP, Punjab, Haryana 4.5 to 4.8 Kerala, North East, hills 4.0 to 4.5 ROUGH CHECK 1 kW makes about 4 units a day, or 1,400 to 1,600 units a year.

What this assumes

  • Sun hours are yearly averages for your region. Monsoon months give much less, winter gives more.
  • The 0.75 loss factor is normal for a good installation. A poor one is worse.
  • Assumes your roof faces roughly south with no shade. Shade changes everything.
  • Assumes a normal grid-connected system with no battery.
  • Your bill may include fixed charges that solar cannot reduce.

Common questions

What size solar do I need for my house?

A common Indian home using 250 to 350 units a month needs about 2 to 3 kW. Use your actual bill for a proper number. Do not go by house size, go by units consumed.

How many units will 1 kW make?

About 4 units a day in most of India, so around 120 units a month and 1,400 to 1,600 units a year. Rajasthan and Gujarat get more, Kerala and the North East get less.

Should I install a bigger system than I need?

Usually not. Subsidy stops at 3 kW, so extra size costs full price. And if your state does net billing instead of net metering, your extra units are bought back at a low rate. Match the system to your usage.

Where do I find my monthly units?

On your electricity bill, look for units consumed or kWh. If you cannot find it, enter your bill amount instead and we will work backwards from your state tariff.

Data last reviewed August 2026 Full methodology Disclaimer