Watts per sq ft when using led

I have a 300w led that draws around 130 watts.
My grow room is 2ft by 2.5 ft or 5 sq ft.

I have one plant.

Do I need to make my grow room smaller so I have enough Watts per sq ft?

Maybe knock 6 inches off the width so I’m at 2x2 or 4 sq ft ?


The rule of thumb I used is 50w per square foot. Your space is 5 sq ft. You would need about 250 true watts to light your area. Amazon has deals all the time for 300w leds (120-130w actual) for less than $75. I wouldn’t make the space any smaller simply because 1 plant lighted sufficiently can easily fill that space. I’m a new grower myself so take it for what it’s worth. Just what I would do. :sunglasses:

You can veg your plant under that light but you may come up a little short when you switch to flower.


I will tag @dbrn32 to help answer. I have heard between 35 and 50 true wats for LEDs. I try to stay at 50 per sq ft. I would say for 5’ long. I would be looking at 2 300s. I use 2 450s “200 actual wats each” side by side for a 4’ tent. I normally only have plants on one side of the tent. The foot print for my 300 is only 1 1/5 foot square for flowering. 2’ square for the 450. just as a reference.

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Thanks you two.

I will keep my 300w led that has a 132w actual and my 5 sq ft space for this first grow and add more light if need be.

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I have had great luck with the vipar 450s. How ever. With the help of a few members on here. they can help you get you some superior lights for a great price. And also use less wats to get more light.

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Ya, this is my first grow and I only have 5 weeks then I think I need to shut it down because if a 10 day trip.

I’m just going through the motions now to get a better understanding of all of this and I didn’t want to wAit 2 months before I start.

If the plant gets big in veg with the one light cool… if not, I will buy a bigger light.

A friend of mine just left his plant alone while taking a 7 day trip. he expected it to be dead when he got back. He is in coco to make it worse. He got back and the plant looked great. I would just water heavy before you leave, and you may be fine if you can’t get some one to look after it for you. In coco they should be watered every day. Soil gives you more of a cushion, time wise.

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Good to know. I was planning on a good watering prior to leaving and then setting up a drip system but first I need to see how much the plant drinks.

I can’t leave the lights on though, I would be stressed out about a fire or some non sense happening while on vacation.

I do get full sun for 8 hrs a day though so we will see what happens.

I’m also in SoCal and it’s about to get hot so that’s another issue with growing now.

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I think you missed the crucial part there, he has ONE plant so that’s all he has to light up, not get a good coverage across the whole room.

In other words, @erich, think of how much space that one plant will take up, it will be unlikely to clear 3 sq.ft so I reckon you are good for the light hanging over that single plant.

Start adding more plants, you’ll need more light.

Edit to add: Example. The room I grow in is 4’x3’x10’, so you think “12 sq ft” or 600 actual watts. But I’m only growing a single plant under my LED light, and she’s happy under my 137w actual watts setup (soon to be slightly improved), have a 4-to-1 splitter I can put LED or CFL bulbs in for a second plant should I wish. I want to go 4 or more plants, I need to add more lighting. So you have to look at more than just the actual space, for there’s no sense in lighting up most of an empty room fully.


Good to hear… until I have 2 plants…

How do u think 2 small auto flower plants would do in the room w the current light though?

Asking for future reference

Good question, knowing what light you have may help as the variation between these “300w” grow lights is enormous as you go from manufacturers

Oh - it’s this one.

Do you think @erich can flower his plant under 1 of those? Wouldn’t bud density suffer? I’m in no way any kind of expert.

I reckon so, this is what I have under 137w real watts of LED


If you go with roleadro, I recommend the 2nd generation version. I have 2 of them and they work good

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Watts is a unit of power and takes no consideration for the electrical efficiency or efficacy of your lighting. There are people on this site growing damn good looking plants at 25 watts per square foot. However, you can bet they didn’t buy their lights on amazon either.


I have two lights for a total of 440w wall-draw in a 4x4 tent, that’s only 27.5W per sq foot. Only scared about burning them flowering at 18"-24"
Seems like that’s a good light for a 2x2 space,“132w actual” should workout OK.
But i’m just a noob-grower not an old salty master grower like many of them here" Just a Master Smoker" :muscle:


I’ve got my 24 square feet illuminated with 360 total watts with my diy lights and the plants look happy.

FYI: you don’t need as much intensity during veg as you will in late flower.


Ya I read that too. This is my first grow my lights are at 24 in above plant.

I think I have a note to bring the lights down to 12-15 in when we start to flower.


50 watts per square foot is a decent rule of thumb if you have CFLs, HID, or Amazon blurple lights. If you have some high end COB or strip lights, you can probably get by with as little as 35 watts per square foot, because they put out more light per watt. They can veg fine with half that, but they take longer. Go to flower with less and you will get poor yields and wispy buds.

If you can’t afford to buy enough lights, it’s better to shrink the lighted area to get your watts per square foot up to par. (Pun intended.)