Solar Rooftop Calculator: How Many Solar Panels Can Fit On Roof? kW?

“How many solar panels can I fit on my roof?”

That’s a very frequent question by homeowners who want to put solar panels on their roofs. There are a number of solar rooftop calculators are supposedly designed to estimate that; most of them are not all that accurate. That’s why we have created these two very useful resources for everybody who wants to figure out how much solar power can their roof generate:

  • Solar Rooftop Calculator. Here you basically have to input the total roof size, and the calculator will tell you how many 100-watt, 300-watt, or 400-watt solar panels you can put on your roof (theoretical maximum).
  • Number Of Solar Panel By Roof Size Chart. We have calculated how many of either 100-watt, 300-watt, or 400-watt solar panels you can put on roofs ranging from very little 300 sq ft roof to huge 5,000 sq ft roof, and summarized the results in a neat chart.
How Many Solar Panels Can Fit On Roof 10kw solar system
This is a standard 10kW solar system, consisting of 25 400-watt solar panels. As we will see in the summarized chart below, the minimal roof size for a 10kW system is only 800 sq fr roof area (600 sq ft viable for solar panels due to 75% code consideration)

Alright, going from the first principles, here is how you can calculate how many solar panels you can fit on your roof. This also includes all the factors that are applied within the solar rooftop calculator (you can use it further on):

  • Size of your roof. The biggest the roof, the more solar panels you will be able to put on it. You can put solar panels on any roof; be it 300 sq ft, 500 sq ft, 1000 sq ft, 2000 sq ft roof, and so on. The main thing you have to do is to calculate your roof square footage. With flat roofs, that will be easy (just multiply the width by the length). For gable roofs, dutch gable roofs, gambrel roofs, hip roofs, mansard roofs, and shed roofs, you will need to use a little bit of math.
  • Percentage of the roof used for solar panels. You can’t use 100% of your roof for solar panels. How much roof space can you use solar panels? You have to take into account the requirements of the NEC code, building codes (IBC), fire codes (IFC), and structural engineering codes (ASCE). You must allow for a “3-ft clearance down from the ridge of a pitched roof” is an example from the IFC code. In general, when all these codes are applied, we can use about 75% of the total square footage of our roof for installing solar panels.
  • Size of solar panels (or, better yet, watts per square foot of solar panels). Figuring out the standard sizes of solar panels is a tough job as we have pointed out in our article about typical solar panel sizes and wattages here. The smarter way to use the data about how many watts do solar panels produce per square foot. In fact, by averaging different wattages and dimensions of solar panels, we can see that an average solar panel will produce 17.25 watts per sq ft of roof area.

By understanding all these 3 key inputs, we can write the equation for theoretically maximum solar rooftop solar system size like this:

Max. Solar System Size (Based On Roof Size) = Roof Area (Sq Ft) × 0.75 × 17.25 Watts / Sq Ft

When we get the max. solar system size, we calculate how many solar panels we can put on the roof.

Quick Example: Let’s say we have an 800 sq ft rooftop and want to know what size solar system we can install and how many solar panels we can put on that roof. Let’s use the above equation to calculate this:

Max. Solar System Size (800 Sq Ft) = 800 Sq Ft × 0.75 × 17.25 Watts / Sq Ft = 10,350 Watt = 10.35kW Solar System

Now, by average solar panel wattage per square foot, we can put a 10.35kW solar system on an 800 sq ft roof. This is how many solar panels you can put on this roof:

  • If you only use 100-watt solar panels, you can put 103 100-watt solar panels on the roof.
  • If you only use 300-watt solar panels, you can put 34 100-watt solar panels on the roof.
  • If you only use 400-watt solar panels, you can put 25 100-watt solar panels on the roof.

Of course, you can also use other solar panel wattages and a combination of different wattage solar panels.

This is just one example. To help you adequately estimate the size of the solar system and the number of solar panels you can put on your roof, you can use the following Solar Rooftop Calculator. Further on, we have also calculated how many solar panels you can put on 300 sq ft to 5,000 sq ft roofs, and summarized the results in a big chart you can freely use:

Solar Rooftop Calculator (Max. Solar System Size, Number Of Solar Panels)

 

Here is how you can use this solar rooftop calculator to determine the solar system size and number of 100-watt, 300-watt, or 400-watt solar panels you can place on your roof:

Let’s say you have a 600 sq ft roof. You want to put solar panels on (due to 75% available area, the viable roof area is 450 sq ft, the calculator accounts for that). Just slider the slider to ‘600’ and you get the results:

You can put a 7.763 kW solar system on a 600 sq ft room. If you use only 100-watt panels, you will be able to fit 77 of them on the roof. If you use only 300-watt panels, you will be able to fit 25 of them on the roof. If you use only 400-watt panels, you will be able to fit 19 of them on the roof.

Here are the calculated number of panels you can put on various-sized rooftop, summarized in the before-mentioned chart:

Roof Solar System Size And Number Of Panels Chart

Roof Area (Square Footage): Max. Solar System Size: Max. Number Of 100 Watt Solar Panels: Max. Number Of 300 Watt Solar Panels: Max. Number Of 400 Watt Solar Panels:
300 Square Feet Roof: 3.881 kW Solar System 38 Of 100 Watt Solar Panels 12 Of 300 Watt Solar Panels 9 Of 400 Watt Solar Panels
350 Square Feet Roof: 4.528 kW Solar System 45 Of 100 Watt Solar Panels 15 Of 300 Watt Solar Panels 11 Of 400 Watt Solar Panels
400 Square Feet Roof: 5.175 kW Solar System 51 Of 100 Watt Solar Panels 17 Of 300 Watt Solar Panels 12 Of 400 Watt Solar Panels
450 Square Feet Roof: 5.822 kW Solar System 58 Of 100 Watt Solar Panels 19 Of 300 Watt Solar Panels 14 Of 400 Watt Solar Panels
500 Square Feet Roof: 6.469 kW Solar System 64 Of 100 Watt Solar Panels 21 Of 300 Watt Solar Panels 16 Of 400 Watt Solar Panels
550 Square Feet Roof: 7.116 kW Solar System 71 Of 100 Watt Solar Panels 23 Of 300 Watt Solar Panels 17 Of 400 Watt Solar Panels
600 Square Feet Roof: 7.763 kW Solar System 77 Of 100 Watt Solar Panels 25 Of 300 Watt Solar Panels 19 Of 400 Watt Solar Panels
650 Square Feet Roof: 8.409 kW Solar System 84 Of 100 Watt Solar Panels 28 Of 300 Watt Solar Panels 21 Of 400 Watt Solar Panels
700 Square Feet Roof: 9.056 kW Solar System 90 Of 100 Watt Solar Panels 30 Of 300 Watt Solar Panels 22 Of 400 Watt Solar Panels
750 Square Feet Roof: 9.703 kW Solar System 97 Of 100 Watt Solar Panels 32 Of 300 Watt Solar Panels 24 Of 400 Watt Solar Panels
800 Square Feet Roof: 10.350 kW Solar System 103 Of 100 Watt Solar Panels 34 Of 300 Watt Solar Panels 25 Of 400 Watt Solar Panels
850 Square Feet Roof: 10.997 kW Solar System 109 Of 100 Watt Solar Panels 36 Of 300 Watt Solar Panels 27 Of 400 Watt Solar Panels
900 Square Feet Roof: 11.644 kW Solar System 116 Of 100 Watt Solar Panels 38 Of 300 Watt Solar Panels 29 Of 400 Watt Solar Panels
950 Square Feet Roof: 12.291 kW Solar System 122 Of 100 Watt Solar Panels 40 Of 300 Watt Solar Panels 30 Of 400 Watt Solar Panels
1000 Square Feet Roof: 12.938 kW Solar System 129 Of 100 Watt Solar Panels 43 Of 300 Watt Solar Panels 32 Of 400 Watt Solar Panels
1100 Square Feet Roof: 14.231 kW Solar System 142 Of 100 Watt Solar Panels 47 Of 300 Watt Solar Panels 35 Of 400 Watt Solar Panels
1200 Square Feet Roof: 15.525 kW Solar System 155 Of 100 Watt Solar Panels 51 Of 300 Watt Solar Panels 38 Of 400 Watt Solar Panels
1300 Square Feet Roof: 16.819 kW Solar System 168 Of 100 Watt Solar Panels 56 Of 300 Watt Solar Panels 42 Of 400 Watt Solar Panels
1400 Square Feet Roof: 18.113 kW Solar System 181 Of 100 Watt Solar Panels 60 Of 300 Watt Solar Panels 45 Of 400 Watt Solar Panels
1500 Square Feet Roof: 19.406 kW Solar System 194 Of 100 Watt Solar Panels 64 Of 300 Watt Solar Panels 48 Of 400 Watt Solar Panels
1600 Square Feet Roof: 20.700 kW Solar System 207 Of 100 Watt Solar Panels 69 Of 300 Watt Solar Panels 51 Of 400 Watt Solar Panels
1700 Square Feet Roof: 21.994 kW Solar System 219 Of 100 Watt Solar Panels 73 Of 300 Watt Solar Panels 54 Of 400 Watt Solar Panels
1800 Square Feet Roof: 23.288 kW Solar System 232 Of 100 Watt Solar Panels 77 Of 300 Watt Solar Panels 58 Of 400 Watt Solar Panels
1900 Square Feet Roof: 24.581 kW Solar System 245 Of 100 Watt Solar Panels 81 Of 300 Watt Solar Panels 61 Of 400 Watt Solar Panels
2000 Square Feet Roof: 25.875 kW Solar System 258 Of 100 Watt Solar Panels 86 Of 300 Watt Solar Panels 64 Of 400 Watt Solar Panels
2100 Square Feet Roof: 27.169 kW Solar System 271 Of 100 Watt Solar Panels 90 Of 300 Watt Solar Panels 67 Of 400 Watt Solar Panels
2200 Square Feet Roof: 28.463 kW Solar System 284 Of 100 Watt Solar Panels 94 Of 300 Watt Solar Panels 71 Of 400 Watt Solar Panels
2300 Square Feet Roof: 29.756 kW Solar System 297 Of 100 Watt Solar Panels 99 Of 300 Watt Solar Panels 74 Of 400 Watt Solar Panels
2400 Square Feet Roof: 31.050 kW Solar System 310 Of 100 Watt Solar Panels 103 Of 300 Watt Solar Panels 77 Of 400 Watt Solar Panels
2500 Square Feet Roof: 32.344 kW Solar System 323 Of 100 Watt Solar Panels 107 Of 300 Watt Solar Panels 80 Of 400 Watt Solar Panels
2600 Square Feet Roof: 33.638 kW Solar System 336 Of 100 Watt Solar Panels 112 Of 300 Watt Solar Panels 84 Of 400 Watt Solar Panels
2700 Square Feet Roof: 34.931 kW Solar System 349 Of 100 Watt Solar Panels 116 Of 300 Watt Solar Panels 87 Of 400 Watt Solar Panels
2800 Square Feet Roof: 36.225 kW Solar System 362 Of 100 Watt Solar Panels 120 Of 300 Watt Solar Panels 90 Of 400 Watt Solar Panels
2900 Square Feet Roof: 37.519 kW Solar System 375 Of 100 Watt Solar Panels 125 Of 300 Watt Solar Panels 93 Of 400 Watt Solar Panels
3000 Square Feet Roof: 38.813 kW Solar System 388 Of 100 Watt Solar Panels 129 Of 300 Watt Solar Panels 97 Of 400 Watt Solar Panels
3100 Square Feet Roof: 40.106 kW Solar System 38 Of 100 Watt Solar Panels 38 Of 300 Watt Solar Panels 38 Of 400 Watt Solar Panels
3200 Square Feet Roof: 41.400 kW Solar System 414 Of 100 Watt Solar Panels 138 Of 300 Watt Solar Panels 103 Of 400 Watt Solar Panels
3300 Square Feet Roof: 42.694 kW Solar System 426 Of 100 Watt Solar Panels 142 Of 300 Watt Solar Panels 106 Of 400 Watt Solar Panels
3400 Square Feet Roof: 43.988 kW Solar System 439 Of 100 Watt Solar Panels 146 Of 300 Watt Solar Panels 109 Of 400 Watt Solar Panels
3500 Square Feet Roof: 45.281 kW Solar System 452 Of 100 Watt Solar Panels 150 Of 300 Watt Solar Panels 113 Of 400 Watt Solar Panels
4000 Square Feet Roof: 51.750 kW Solar System 517 Of 100 Watt Solar Panels 172 Of 300 Watt Solar Panels 129 Of 400 Watt Solar Panels
4500 Square Feet Roof: 58.219 kW Solar System 582 Of 100 Watt Solar Panels 194 Of 300 Watt Solar Panels 145 Of 400 Watt Solar Panels
5000 Square Feet Roof: 64.688 kW Solar System 646 Of 100 Watt Solar Panels 215 Of 300 Watt Solar Panels 161 Of 400 Watt Solar Panels

As you can see, our roofs have a big solar power generating capability. Now you can just look at this chart to get an idea of how many solar panels will fit on your roof.

Let’s take a big 2000 sq ft roof as an example. Such a big roof has 1500 sq ft of viable solar panel area. If each of these viable square feet generates 17.25 watts of electricity, the combined 1500 sq ft will be able to generate more than 25kW per peak sun hour (25.875kW, to be exact).

To construct such a system, you will have to either place 258 100-watt solar panels, 86 300-watt solar panels, or 64 400-watt solar panels on your roof. If you check the chart for the 2000 sq ft roof area, you can see that all these numbers are right there.

With the solar rooftop calculator and this chart, you have two very useful tools to figure out what size solar system you can put on your roof and how many solar panels you will need for that. If you have any questions or suggestions, you can use the comment section below, give us some numbers, and we will help you out.

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