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How Many LED Watts Are Required Per Square Foot of Grow Space?

on September 08, 2014

The Ultimate Guide to Help You Choose the Correct LED Wattage for Your Grow Space (during flowering)

*Article updated May 2018

Are you new to the world of LED growing? If so, the charts below will help you determine how much energy (by wattage) your plants require for flowering.

Disclaimer: Wattage is a relic of the HID (MH and HPS) days. Wattage should not be used to determine the coverage area a fixture or the usefulness of an LED grow light. Wattage should only be used as a simple method for approximating the correct fixture size for your grow. 

PPFD (umol/j/m2) and DLI is the correct metric for measuring useful light intensity over a given area. Coupled with the correct spectrum for your plant type and phase of growth, PPFD (and spectrum) are the keys to a successful grow. However, for the purpose of estimation, we will report wattage calculations in this article.

When we talk about wattage inthis article, we are referring to the wattage drawn at the wall, not what the manufacturer states as "LED wattage" - which is typically the product of the maximum LED wattage and the number of LEDs. For example, 300 x 3-watt diodes would be a 900 watt LED grow light. However, the LED grow light might only draw 500 watts at the wall.

Grow variables

It is important to understand that the number of actual watts that you need for your grow will vary depending on:

    • Plant type (high light or low light)
      • High light plants - i.e. tomatoes, peppers, etc
      • Low light plants - i.e. herbs and leafy greens (such as basil lettuce)
    • Growth phase
      • Seedlings, vegetative, and flowering plants all require a different amount of light
    • Total area of your grow
      • A larger grow area will require more power

Watts per square foot

    The average LED grow light draws about 32 watts to cover 1 sq ft for flowering. Compare this to a typical HID fixture which rings in at 40 watts per square foot (assuming a  5’ x 5’ area, or 25 sq ft coverage area). Using an HID in a 4’ x 4’ will bring the power coverage up to 62.5 watts per sq ft. (The energy saving that growers can expect from using LED grow lights instead of HID is around 38%. This energy savings only takes into account to savings growers gain when using LEDs fixtures. It does not account for other environmental factors where growers can save energy. For example, less ventilation and air conditioning may be used, or foregone completely, depending on the size of the setup and ambient temperatures. Total power savings may rise above 50% in certain scenarios.)

    Different LED grow lights will have different efficiencies. More efficient LED grow lights will use fewer watts to emit the same amount of light that a less efficient LED grow light will exude. Therefore, as mentioned above, wattage is not the most accurate tool to know how powerful of a grow light you need for a particular coverage area.

    LED Wattage Chart Explanation

    The wattages listed below assume you are flowering your plants. If vegging, you might consider reducing your wattage by 50% since vegging plants only require about half the light intensity. As always, it is best practice to follow the manufacturer's recommendations.

    Using the charts

    In each chart you will find the following columns:

        • '# of Plants' to be grown
        • Square footage that the respective number of plants cover
        • Recommended LED wattage for the number of plants grown in the respective space

     

    Wattage charts

    Assume about 32 watts/sq ft (actual LED wattage) for flowering. Fewer watts might equate to smaller yields while more wattage may lead to larger yields.

     

    Quick Guide (watts per coverage area)

    1' x 1': 32 watts (~30 to 40 watts)

    2' x 2': 128 watts (~120 to 140 watts)

    2' x 4': 256 watts (~240 to 300 watts)

    3' x 3': 288 watts (~250 to 300 watts)

    4' x 4': 512 watts (~500 to 650 watts)

    5' x 5': 800 watts (~700 to 900 watts)

    4' x 8': 1024 watts (~900 to 1100 watts)

    6' x 6': 1152 watts (~1000 to 1200 watts)

     

    Recommended wattage assuming 1.0 sq ft/plant

     # of Plants   Square Feet   Wattage from Wall
    1 1 30 to 40 watts
    2 2 60 to 80 watts
    4 4 120 to 140 watts
    6 6 180 to 200 watts
    8 8 240 to 300 watts
    10 10 300 to 340 watts

     

    Recommended wattage assuming 2.0 sq ft/plant

     # of Plants   Square Feet   Wattage from Wall
    1 2 60 to 80 watts
    2 4 120 to 140 watts
    4 8 240 to 300 watts
    6 12 360 to 400 watts
    8 16 500 to 650 watts
    10 20 600 to 800 watts

     

    Recommended assuming 4.0 sq ft/plant

     # of Plants   Square Feet   Wattage from Wall
    1 4 120 to 140 watts
    2 8 240 to 300 watts
    4 16 500 to 650 watts
    6 24 700 to 860 watts
    8 32 900 to 1100 watts
    10 40 1100 to 1400 watts

      

    Shop LED Grow Lights ›  

     

    Related: What is PAR, PPF, DLI and Efficacy? Light Factors for Your Indoor Plants - Explained!

    Related: See what else you should consider before purchasing a LED grow light 

     

     

    Disclaimer: All LED grow light 'Descriptions' and 'Specs' stated by LED Grow Lights Depot are the claims of the original manufacturer and/or supplier and not LED Grow Lights Depot. We do our best to ensure the information is accurate and correct.

    Notes: Please be aware that the cultivation of certain plants may or may not be legal within your own specific region or country. LED Grow Lights Depot does not encourage or condone any illegal activity and advises each individual / user to inform themselves of the relevant laws within their own region/country.

    26 comments
    by Albie on August 09, 2018

    My grow area is 40feet by 8 feet or 320 square feet
    How many plants can i grow
    And how many lights do i need

    by Ozz on August 09, 2018

    Well go to Walmart online and you can get a LEDs for 80 to a100 bucks. I got a 1200 watt light I use more white and blue,then I got 2 _ 600 watt LEDs to. if you buy to 600 watt lights ( more red) you can cover more area being they shine straight down. These lights use very little power to running so 2400 watts cost 200 buck and maybe run power bill up 10 bucks. Note that keeping the light around 18 inches above your plants because you can burn then! Also the higher to put it the less stretching on your plant which mean tighter Leaf space which equal more flowers.

    by Mark on July 08, 2018

    40 yrs exp.and sometimes less is more .Seedling n young clones need less more difused light so just old shop lights to start then add in or change up to led or what ever.

    by John on January 01, 2018

    What you have to remember, there is a direct relationship between true wattage and plant mass example it doesn’t matter what your growing, so if we say you have 4 plants and you are providing 600 watts of light and you get 40oz of dry plant matter, for ease of convenience you get 10oz per plant, so lets say now you add 4 more plants under the same wattage you will still get 40oz of dry plant matter it will be distributed amongst the 8 plants in the form of 5oz per plant, so if you want more plant mass (fruit) you have to feed them more wattage its that simple. Using LEDs always look at the true wattage drawn from mains, and not what the manufacturer claims is the wattage,

    by eh terry on December 07, 2017

    Well it is almost 2018 and 100 bucks will get you the latest full spectrom 600 watt grow light.
    But you could want to customize for your application.

    by The REAL ''The Dude'' on September 19, 2017

    Ok this is pretty stupid. It’s 2017 now. It is VERY easy to get a GREAT LED customized to the spectrum YOU want. Go to amazon, you can buy a 600w LED for 100 bucks. You may say ‘’thats a cheap led’’. Ok, it has all the spectrums I ASKED THEM FOR and it has lasted me over a year. Do you think 100 bucks for an led that last for a year is more of a waste than a 400 dollar LED light that last 2 years?

    LED lights have come a long way. They produce less heat, can be brought closer to the plants and cost less than HID. Penetration is no longer an issue because of these facts. You can bring the light very close to your plants without detrimental effect. A little training and your light easily reaches anywhere you want as long as its has the watts for it. If you know how to train correctly, you can get away with a lot less watts too but we’re not here for that.

    All I’m saying is that you can get AMAZING results with a 100 dollar LED from amazon. There is no reason to buy anything else with the prices of these things now days. Go with what has the most reviews and make sure there is a return option.

    LEDS

    Cost less money to buy AND operate
    Creates less heat
    Can be brought lower to the plants without burning
    Last longer than HID
    Take up way less space
    Can be customized to your specific light wavelength

    by james reeves on June 12, 2017

    don’t waist money on expensive LED lights. i bought 150 watt LED “flood” lights at Lowes. they were $20 a pair. i purchased the metal round hangers where i inserted one bulb. i hung the lights on a rope 2 feet above the vegetative plants. the lights are about 2 feet apart on the rope. each came with a clip that can attach to rope. in an 8 foot area i have four 150 watt LED flood light hanging above the plants. the lights are on 24/7. my plants grow 3 inches every two days or about. The metal light fixtures cost about $6 at Lowes. two bulbs and two fixtures cost me about $52. plants grow very well.

    by Lostalot on March 17, 2017

    So what’s better a 4ft by 8ft tent or a 6ft by 6ft tent and will a single 200 watt led light be sufficient for my tent

    by michel on March 10, 2017

    Sorry to say but didnt see any useful info here
    plants dont give a damn about lumens …they want umoles …in specific wavelenghts…
    leds dont look as bright(flashy ?) as hps because there is no glare …from the bulb.
    people get em too close and stunt or burn their plants …lack is the far far red spectrum(black body) which is heat…quartz halogen can compensate for that in moderation (bloom) and there is no correlation between ‘’ how many plants’’ and led wattage…stuff 50 clones in a 2×2 even with a 1000 true watts led and they will all fall short or die ..cos they know the spatial space they occupy, and overcrowding is not their forte…and lets be honest top bin leds are like gold to lighting companies they are even reserved in advance and its not for grow lights that you get on the internet …those high end leds get you to spend mostly on cooling..and efficient led drivers , the leds themselves are very rarely top bin , so to give a better bang for the buck they fine tune the surroundings…dont be fooled and build yourselves a light , make it adlustable to your own needs and genetics the price will be about the same…but the overall quality will be better good day

    by Johnb341 on January 22, 2017

    I simply couldn’t depart your web site prior to suggesting that I actually loved the usual info a person supply for your guests? Is gonna be again continuously in order to check up on new posts. fgdgededdcgk

    by Andre on October 17, 2016

    So if i grow 16 plants on 11 sq. What do i need in watts?

    by Tarey on October 06, 2016

    Seedlings do better with T8 lights. I grow mine in red cups until the root is really filling the cup. The T8 grows many more internodes than LED which gets your plant off to a great start. I clone first in a clone bucket – super great. Then when I transplant from the red cups, it’s into a gallon and 1/3 sized container. Same thing with the roots, let them grow into the container. When they are 1’ to 18" I transplant one last time into a 3-5 gallon container. I let them get comfortable and start to grow again. Then I set to flower. I’ve got 2 6 × 6 tents and I have about 1200 LED watts worth of UFO lights in each. Not much heat and I can lower and raise according to need. In one tent, instead of UFOs I have a Mars Hydro 144 in the middle – that’s 300 LED watts, though covering a larger area. LED is the best way to grow and flower, the taste, smell of your herbs are amazingly better. Starting with T8 there are many more internodes, i.e. places for flowers later. Or for cutting clones off. Don’t overpay for LED lights, because prices should be coming down not going up on these. A 300 watt light shouldn’t cost $1000! Shop around. Most ufo light dealers on ebay are great, I’ve bought from a few. They list the number of LED lights, the color and what it is good for. They can give great yields of top shelf herbs which is what you want. Some with UV etc even help chase away the evil mites. Good luck.

    by Zane on October 01, 2016

    Whats a good estimate on amount of plants to put under 1000w full spectrum led 15 inches wide light

    by lindsay Branscombe on August 15, 2016

    My question is the same as Kevin’s. Why are you using watts to talk about LEDs. Doing this chart (which could be SUPER helpful) with watts instead of lumens leaves the question of whether or not you’re talking about the actual wattage required to run the bulb or the “watt equivalent” of a typical bulb. ie: are you talking about an LED that requires 50 watts of power? Or are you saying an LED that produces the same amount of lumens as a typical 50watt bulb?

    by sheetal borkar on July 18, 2016

    The LED grow light market is expected to rise to more than $1.9 Billion by 2020, growing at a Compound Annual Growth Rate (CAGR) of 26.93% between 2015 and 2020.

    http://www.marketsandmarkets.com/pdfdownload.asp?id=237907331

    by kevin on July 03, 2016

    why are you talking about wattage? plants use lumens. So, If have a system that can create more lumens with less energy input (wattage) that is the goal. which LED lights can achieve with computer chips. lumens = photosynthesis. watts are the input of energy to run the equipment that produces lumens. So question I ask is How many lumens do I need per square foot? The sun right is probably suppling well over 12000 lumens ?

    by Macy not putting on May 19, 2016

    macynoelle2013@gmail.com

    by Macy not putting. on May 19, 2016

    i understand that your suppose to keep the walls as close to your plants (or in other words keep them in an area that makes sense as to how many plants you have.) but in my case i have bought a larger grow tent than i needed but i wanted room for if i ever decided to grow more. but anyways im only growing about 6 plants and i have a 16 foot area how many watts would you say i need? i am have extreme trouble with this please email me!!!!!!!!!!

    by michael frazier on April 03, 2016

    the black dog is a far more superior Led with its range and full spectrum. with veg range Phytomax 600 veg range 6×6 flower range 4×4

    by Koki on February 02, 2016

    smd leds are not suitable for growing, un need to look for power leds.
    in addiction, led bulbs emit light on a very specific frequency, one kind of blue and one kind of red are not enough. you need at least 440nm and 480nm on the blue and 640nm and 680nm on the red

    by Marsha Seitz on January 14, 2016

    I have a tower garden which did great outside this past summer. Around the garden I put 4 4 foot strips of 9 blue 27 red 5watt each. Description says 15w 36 smd 5050. Is this enough to grow my plants. They aren’t doing so well.

    by Larry on January 09, 2016

    Good info thanks

    by Jared on December 23, 2015

    New to LED scene kinda, cuz I got duped on Amazon for SUPPOSED FULL SPECTRUM 145watt UFO style.. It killed my seedlings. I think it was a bloom bulb, it was VERY pinkish/red. I assume missing the blues of the real deal LEDs out now I see, more of whitish purplely pink.. Lol. Trying to not go over 300$ as this will only raise 1 to 2 sour x kush beans I got a handful of from last season.. Will most likely fim, then LST them (my usual method-get 4 or more fat kolas, but THEN install a simple PVC scrog to up yield of only 2 plant harvests.. As a personal use grower, I can say LED may be the future guys..not everyone can outfit an exhaust system w carbon scrubber anywhere they please.. As far as I know their self cooled n all that’s needed is a fan for circulation.. I hope these new LEDs work better then my last 130 investment.. Trying to hit like 250$ n e advice appreciated

    by Zlotvor on December 08, 2015

    Those numbers are exactly what I’ve found in my experiments.
    With real 65W in 0.5×0.5 meter space I’m growing 65-70g of nice flowers

    by handsome pat on November 26, 2015

    I’m getting some real good information thank you very much

    by the dude on October 07, 2015

    top notch info thanks!

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