What fits on your roof
How much roof does 1 kW of solar need?
Plan on about 100 sq ft of shade-free roof for every kW. The panels themselves take roughly half of that; the rest is the gap between rows so they don’t shade each other, and a path to walk and clean. A 3 kW system needs about 300 sq ft, roughly a 15 × 20 ft terrace.
| System | Roof area (sq ft) | Panels of 540 Wp | Units a month |
|---|---|---|---|
| 1 kW | 100 | 2 | 120 |
| 2 kW | 200 | 4 | 240 |
| 3 kW | 300 | 6 | 360 |
| 4 kW | 400 | 8 | 480 |
| 5 kW | 500 | 10 | 600 |
| 10 kW | 1,000 | 19 | 1,200 |
How big is a solar panel?
Most home systems in 2026 use panels of 540 to 580 Wp. A 540 Wp panel measures about 2.27 × 1.13 m, or 7.5 × 3.7 ft, roughly 28 sq ft. Smaller 330 to 400 Wp panels still exist but you need more of them for the same kW. Every common size, in mm and feet, with weights, is in our solar panel size chart.
Measuring your roof
- Measure length and width in feet and multiply. Do it for each open section separately.
- Leave out the water tank, stairs, parapet edges and any part in shade between about 9 am and 4 pm.
- South-facing space is best. East and west facing roofs work but make somewhat less.
- A tin or asbestos roof needs a different mounting; tell the installer before the survey.
Frequently asked questions
How many square feet do I need for a 3 kW solar system?
About 300 sq ft of shade-free roof, enough for six 540 Wp panels with walking space.
How many solar panels are needed for 3 kW?
Six panels of 540 Wp make 3.24 kW. With 400 Wp panels you would need eight.
Can I fit 5 kW on a 400 sq ft roof?
At 100 sq ft per kW it fits just under 4 kW: seven 540 Wp panels, or 3.8 kW. A 5 kW system needs around 500 sq ft; an elevated structure can help on a crowded terrace.
What is the size of a 540 watt solar panel?
About 2,272 × 1,133 mm, or 7.5 × 3.7 ft, based on current datasheets.
Know the size? See the price and payback in the solar calculator. Our assumptions are on how we calculate.