Solar Panel Watts Per Square Foot: ‘We (Finally) Did The Math’

Alright, a lot has been said about solar panel watts per square foot. Everybody agrees this is a very important specification. There is a lot of disagreement on how many watts can solar panels produce per square foot.

Some say as little as 10 watts per square foot; others say it’s 20+ watts per square foot. The truth, as usual, is somewhere in between.

Solar Panel Watts Per Square Foot
This “how many watts per square foot of solar panels” question is quite puzzling. That’s why we did the math (finally).

We took a statistical analysis approach to once and for all answer what is the solar panel output per square foot definitively. Translation: We did the math. On top of that, we are going to look at Tesla solar roof watts per square foot, since that roof is considered to have an above-average wattage output per square foot.

Here is the simple plan that will help us to calculate the average energy output of solar panels per square foot. It’s a 3-step process:

  1. Check the standard solar panel size (area) and the output wattage of the whole panel.
  2. Divide the solar panel wattage (for 100W, 150W, 170W, 200W, 220W, 300W, 350W, 400W, 500W) by the solar panel area to get the solar panel output per square foot for a specific solar panel. Here is the equation: Solar Output Per Sq Ft = Panel Wattage / Panel Area.
  3. To get the average solar panel watts per square foot, just average the resulting specific solar panel average solar output per sq ft.

Sounds reasonable, right?

Alright, we have gathered the typical sizes (areas) of 10 different wattage solar panels ranging from 100-watt to 500-watt panels. We have calculated the solar output per square foot for each of these standard-sized panels, and gathered the results in this chart:

Solar Panel Output Per Square Foot Chart For 100W – 500W Panels

Solar Panel Wattage (Watts): Area (Square Feet): Watts Per Square Foot:
100 Watts 6.07 Square Feet 16.47 Watts Per Square Foot
150 Watts 9.34 Square Feet 16.06 Watts Per Square Foot
170 Watts 10.92 Square Feet 15.57 Watts Per Square Foot
200 Watts 11.92 Square Feet 16.79 Watts Per Square Foot
220 Watts 12.64 Square Feet 17.41 Watts Per Square Foot
300 Watts 16.50 Square Feet 18.18 Watts Per Square Foot
330 Watts 17.74 Square Feet 18.60 Watts Per Square Foot
350 Watts 19.45 Square Feet 17.99 Watts Per Square Foot
400 Watts 21.53 Square Feet 18.58 Watts Per Square Foot
500 Watts 27.50 Square Feet 18.18 Watts Per Square Foot

Just from this, we have a good idea of how many watts per square foot we can expect from solar panels. As we can see from the chart (3rd column), the watts per square foot range from 15.57 to 18.60.

Now we just have to implement the 3rd step: Average these numbers. Here is the calculation of the average solar panel watts per square foot:

Average Solar Panel Output Per Square Foot = (16.47 W/sq ft + 16.06 W/sq ft + 15.57 W/sq ft + 16.79 W/sq ft + 17.41 W/sq ft + 18.18 W/sq ft + 18.60 W/sq ft + 17.99 W/sq ft + 18.58 W/sq ft + 18.18 W/sq ft) / 10 = 17.25 Watts Per Square Foot

Here we have a definitive answer; on average, solar panels produce 17.25 watts per square foot.

We are going to look at how Tesla’s solar roof compares to this average. First of all, let’s show one useful application of this number:

Let’s say that we want to know solar panel area per kW. Basically, how much roof area is needed to install 1kW system?

We just divide 1kW or 1000W by 17.25 watts per square foot to get the roof size in square feet like this:

1kW Solar Panel Area = 1000W / 17.25W Per Sq Ft = 57.97 Square Feet

As we can see, we need almost 60 square feet of roof area for a 1kW system (57.97 sq ft, to be specific). Of course, this doesn’t include the structural codes we need to be careful about. For a full answer on how many solar panels you can fit on a roof, you can check this solar rooftop calculator.

Now, let’s have a look at Tesla solar roof:

Tesla Solar Roof Watts Per Square Foot

Tesla solar roof is a bit divisive as well; some people love it, and others say it doesn’t produce as many kWh as other solar panels.

Well, if we calculate the Tesla solar roof watts per square foot and compare it to the average solar output per square foot (17.25W/sq ft), we can evaluate how good Tesla solar roof panels are objective.

Here are the Tesla roof specs:

  • Tesla roof solar panels have a specified 400W wattage.
  • The length of the panel is 74.4 inches, and the width is 41.2 inches (this includes the frame around the 400W panels).

Let’s calculate the area of the Tesla roof panel:

Tesla Roof Panel Area = 74.4 Inches × 41.2 Inches = 3065.28 Square Inches = 21.29 Square Feet

Now let’s divide the 400W wattage by this area to get the solar output per 1 square foot:

Tesla Roof Panel Watts Per Square Foot = 400W / 21.29 Sq Ft = 18.79 Watts Per Square Foot

We have the result: Tesla roof panels produce 18.79 watts per square foot. Compared to the 17.25 watts per square foot, they produce 8.9% more electricity. That’s quite impressive, actually.


As we have seen, the average watts per square foot that solar panels produce is 17.25 watts per square foot. Tesla roof panels are quite a bit above average (8.9%+, to be exact). Hopefully, now you can use this information for your calculations. If you have any questions or suggestions about this math, you can use the comment section below, and we can discuss it a bit.

3 thoughts on “Solar Panel Watts Per Square Foot: ‘We (Finally) Did The Math’”

  1. The complication is determining the power output per square in real situations. The index should reflect the panel’s performance in natural conditions of temperature, environment, installation, etc.
    It is not about dividing the panel STC power by its area. That has never been a problem.


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