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

January 18, 2022

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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