How Many LED Lights Do I Need for My Grow Room? How to Calculate Your LED Lighting Needs

how many grow room lights do i need

You’re thinking of buying or have an LED grow light, and you need to make sure it’s properly sized for your garden. You’ve come to the right place. We’re the No. 1 online retailer of LED grow lights in the U.S. and we partner with laboratories to independently test LEDs for efficiency, marketing accuracy and overall effectiveness. Let’s use that knowledge to help you succeed in your garden, and maybe you’ll even teach your friends a thing or two.

Let’s start with the most basic ways to calculate what size LED grow light you need and move to the more complicated—and more accurate—methods.

How many LED grow light watts are required per square foot of grow area?

Most people think they need a certain wattage for a grow area. While wattage can be a good approximator for LED coverage, it’s not extremely accurate because coverage is affected by other factors, including how efficient the LEDs are and their beam angle. That said, if you’re a hobbyist growing in a tent or other small space, you can safely use wattage to give you a general idea of the proper LED grow light coverage for your area.

Here’s our quick-and-dirty guide to determine how LED grow light wattage can be sized to the square feet in a grow room or grow tent:

  • Vegetative growth: 20 watts per square foot.
  • Flowering: 30 watts per square foot.

In the table below, you can go up or down (+/-) 10% from the wattage calculations seen here and still have an acceptably sized LED grow light. For example, if we look at the 4’ x 4’ row we can see 480 watts for flowering. Dropping down 10% would be 432 watts, while increasing 10% would be 528 watts. Anything in that range will work well, but remember: The lower the wattage in your garden, the lower your yield.

Grow Room Size Square Feet Veg Wattage Flower Wattage
1’ x 1’ 1 20 watts 30 watts
2’ x 2’ 4 80 watts 120 watts
3’ x 3’ 9 180 watts 270 watts
2’ x 4’ 8 160 watts 240 watts
4’ x 4’ 16 320 watts 480 watts
5’ x 5’ 25 500 watts 750 watts
6’ x 6’ 36 720 watts 1,080 watts
4’ x 8’ 32 640 watts 960 watts
8’ x 8’ 64 1,280 watts 1,920 watts
10’ x 10’ 100 2,000 watts 3,000 watts


How many plants per LED grow light?

A question often posed by new growers—how many plants per LED grow light?—is not the right question. We’ll use an example to explain why. Let’s say you have a 4’ x 4’ grow room with a 480-watt LED grow light. You could grow anywhere between one and nine plants comfortably. Yes, some people like to  grow just one or two monstrous plants per light, and that’s OK.

The better question to ask is whether the LED grow light you’re using is properly sized for the grow area, which we went over briefly in the table above. A common mistake by novice growers is fitting as many clones and vegetative plants in a grow area as possible. If you do that, they’re all growing over one another when it comes time to flower the plants. That can lead to lower yields. Plants need ample space to branch out and grow without running into a lot of other plants in the process.

For more guidance on how many plants you should grow within your given grow space under LEDs, see the reference table below.

Grow Room Size Square Feet Recommended # of Plants in Veg Recmommended # of Plants in Flower
1’ x 1’ 1 Up to 2 1
2’ x 2’ 4 Up to 4 Up to 2
3’ x 3’ 9 Up to 9 Up to 5
2’ x 4’ 8 Up to 8 Up to 5
4’ x 4’ 16 Up to 16 Up to 9
5’ x 5’ 25 Up to 25 Up to 12
6’ x 6’ 36 Up to 36 Up to 20
4’ x 8’ 32 Up to 32 Up to 18
8’ x 8’ 64 Up to 64 Up to 36
10’ x 10’ 100 Up to 100 Up to 48

See Our LED Testing Results and Comparisons

We are having all of the bulbs that we sell tested ourselves and we are sharing all of the data with you! Check out some of the data that we have collected so far.