Grow lights

How Many Watts Do You Need Per Square Foot?

How Many Watts Do You Need Per Square Foot?

grow light bulb

Although the question about how many Watts your grow light needs to be for your grow space is a common one for indoor gardeners. It is slowly becoming an unnecessary question. Especially with the increase in popularity in LED grow lights. Although looking for the Wattage of lights does give you an inclination into the size and intensity of the light, it is not accurate enough information to determine if your LED grow light will be good.

If you are looking for the most effective measurements to help assess a grow light’s performance you should look at the light’s PAR, PPFD, and DLI. To obtain the most optimal light you will need to find out these measurements along with the correct light spectrum.

Growth Variables

Like any project, there are going to be variables and growing plants under LED lights are no different.


Type of Plant: High Light or Low Light?  


Growth Phase: Seedling, Vegetative, Flowering, each of these needs different light exposures. 



Size of Your Grow: The total area of your grow in square feet. Bigger areas need more light; smaller areas need less light. 

indoor farm 

Watts Per Square Foot the Numbers?

As a rough estimation, you’re looking for around 32Watts per square foot. However, with the efficiency of LED grow lights sometimes you can choose different lights within a certain range.   

A simple way to find the correct number of Watts for your indoor garden would be to times the square foot space x 32Watts to find your number of Watts.

For example, if you grow area is 10 square feet:

10x32=320 So I will need a 300-350Watt grow light to cover this space.



When it comes to calculating how many watts you need per square foot there is a rough estimation of 32 per square foot. However, grow projects contain many variables subject to different requirements. You will need to identify the type of plant you have, how much light it needs, what phase of growth it is in and how big is your grow going to be. Once you have discovered each of these you will have a better idea of the number of Watts you need. But it is important to note that PAR, PPFD, and DLI are probably the most important measurements when looking at purchasing a grow light. As these are what will impact the growth of your plant the most.


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