How Many Watts Do I Need to Grow Weed, Using CFL Lights?

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How many watts are too many, and how many are too little?

One concern being tossed around constantly in various forums, search engines and discussions online, wattage.

  ” How many watts do I need to grow weed, using my CFL light bulbs….?”

The answer truly varies, but since you’re here for actionable advice and answers, a good rule of thumb is 50 watts per square foot, at a minimum.

Your amount of square footage, possibly cubic footage, pot size and ideal plant size will determine your optimal wattage.


When it all comes down to getting results, however, what really matters is your particular growing scenario. Take an inventory of the following details regarding your grow, whether current or in the future:

  • The sq footage of your space
  • The size of your pot (height)
  • The width of your plant
  • How your plant is trained (flat or tree-shaped)
  • The results you are looking for (quantity or quality; dense or fluffy)

Let’s explore this topic more in depth; I’ll elaborate exactly what I mean by taking an inventory of details, and why.

The square footage of your space determines much.

Johnny Roe uses a 5x5x5 “Hydro-Hutch” grow tent, which is 125 cubic feet; 25 square feet. He wants to grow 4 plants in his tent. So, to go by the minimum 50 watts per square foot rule, he will assume 6.25 square feet per plant. He’ll also grow two plants under each reflector to save power.

Johnny will need a total of 312.5 watts for each hood–a total of 625 watts of lighting in his grow hood.


The size of your pot matters more than most allude to.

Tall pots increase the height of your plant, while wide pots typically increase the width of your plants. If Johnny chooses to use 2 10-gallon pots (wide, not tall), those two plants will grow wide enough to practically fill the grow tent with foliage. If Johnny  chooses 4-5 gallon pots (tall, not wide), his plants should be expected to grow at least 3-4 feet tall by the end of flowering. This is a much less favorable setup than the 10-gallon setup, for two reasons:

  • The height of the tent is 5 feet, so he will only have 12 inches to work with; which will leave nearly no room for his light, fan, carbon filter, etc. He will run out of room quickly.
  • Since he is using CFL lighting, the light needs to be close to the top and sides of the foliage. Since his plant will grow 3-4 feet tall, the plant as a whole will not get much light, only the buds/leaves at the very top, and the remaining buds will be sparse, airy and most likely not as potent as setup #1. Which leads to the next point….


“Training” your plant will maximize production and increase your harvest.

Now, if Johnny had chosen to “train” his plants in the 5 gallon pots to grow OUT instead of UP, he could’ve used the two 312.5 watt CFL hoods to grow HUGE, sparkling, stinky, dense buds with high CBD and THC–simply by tying the branches down so they grew out instead of up.

So let’s now use those examples in real-world application, shall we? This takes us to point #5:


What type of buds do you want?

Do you want swag or Miracle Smoke? Do you want quantity or do you lean more toward quality? Do you NEED dense buds or will more airy buds be fine? 50 watts per square foot — From experience,  will possibly give you the results you want, but don’t be disappointed if you don’t get the harvest you crave.

75 watts per square foot — From my experience, will give you good results, but they may not necessarily be the results you were looking for, all other things being considered. 100 watts per square foot — In my experience, you are in the realm of facilitating pro-quality bud growth with this many watts. This should produce enough intense light to maximize the plants’ photosynthesis for great results.

150 watts per square foot — This COULD be a point of diminishing returns, but then again, so can 100 watts per square foot! BUT, in my experience, since I’m currently running 150 watts per square foot (300+ watts for every 2 square feet), I can honestly say that my only limitation is light footprint. The intensity is THERE. The final product can NOT be distinguished as CFL-grown in a side by side test with Cannabis grown under an HPS light.



 Give your plants as much light as they can take. If they don’t like it, you SHOULD be able to tell by “reading your” plants. Then you can back of the lumens until you find the amount that is good for your grow; within reason of course. So, again, how many watts do YOU need when growing weed?

It’s entirely up to YOU!

By Robert Narley