The short answer
A well-run home grow under a modern LED should land between 0.8 and 1.2 grams of dried, trimmed flower per watt of actual wall draw. A sealed commercial room with CO2, tight VPD control, and a solid irrigation strategy can reach 1.5 to 2.0 g/W. Numbers above 2 g/W exist, but they are rare and usually carry an asterisk somewhere.
High Yield Cannabis Strains Per Plant: Real Numbers and How to Reach Them
Why grams per watt is a comparison tool, not a target
Yield per watt mixes two things that do not scale together. Yield scales with the total photons your canopy receives. Watts measure power going into the fixture, and a real chunk of that never reaches a leaf. A 320 W bar fixture running at 2.9 umol/J delivers 928 micromoles per second. A 480 W budget light running at 1.9 umol/J delivers 912. The cheaper light draws 50 percent more power and gains nothing. Graded by g/W, the better fixture would look worse.
Optimizing Yield: How Many Grams Per Plant in a 5-Gallon Bucket?
That is the trap. Two rooms with different light efficiency, different canopy sizes, and different veg times are not comparable, even when both post a number.
grams per plant in 5 gallon bucket
Metrics that actually tell you something
- Grams per square foot per cycle. For a modern LED canopy, 40 to 60 g per square foot is strong. 30 to 40 is decent. Below 25 and something is off.
- Grams per kWh. This is the one your power bill and your carbon math care about. It folds in fixture efficiency and cycle length.
- DLI, or daily light integral. The photons your canopy actually receives per day in mol/m2/day. This is the input that moves yield.
The light math behind yield
DLI is the number worth building around. The rough formula: PPFD in umol/m2/s, times hours of light, times 3600, divided by one million. A canopy sitting at 900 PPFD over 12 hours works out to about 38.9 mol/m2/day.
In flower, most rooms run 30 to 40 mol/m2/day without CO2 and 40 to 50 with enrichment. Below roughly 25 you leave weight on the table. Above 55, without matching CO2, nutrition, and airflow, you mostly buy heat and stress.
Photoperiod in flower is not a free dial. Going from 12 to 13 hours adds DLI on paper, but plenty of cultivars get strange about it. I would rather raise intensity and keep the canopy even than stretch the night.
Efficacy matters as much as wattage
Photon efficacy, measured in micromoles per joule, tells you how much usable light a fixture produces from each watt. Budget LEDs sit around 2.0 to 2.4 umol/J. Good bar fixtures run 2.7 to 3.0. Same wall draw, meaningfully more light. Energy and lighting standards groups treat umol/J as the correct yardstick for horticultural fixtures, and they are right to.
Uniformity and canopy depth
A hot center and dim corners waste light. I want readings within 10 to 15 percent across the canopy at the same height. Beyond that, stretchy corners and bleached tops eat your grams per watt. Light that reaches 18 to 24 inches into the canopy, through better spread or side lighting, turns lower nodes into flower instead of larf.
What separates a 1.0 g/W run from a 1.8 g/W run
- Canopy management. Topping, training, and a screen to flatten the canopy. A level canopy is the biggest single jump in yield per watt most growers ever make.
- Genetics. Cultivars that stretch and stack yield more than squat, dense ones. Raw yield and top-shelf bag appeal often pull in different directions, and you get to choose.
- Environment. VPD around 1.0 to 1.5 kPa in flower, leaf temps in the mid to upper 70s Fahrenheit, CO2 at 800 to 1,200 ppm in a sealed room.
- Root zone. Frequent, controlled fertigation with real dryback cycles. Oxygen at the roots converts light into biomass. A soggy pot under 900 PPFD just makes a stressed plant.
- Veg time. Longer veg builds a bigger canopy and more grams, but it also burns more kWh. The g/W figure can fall while total yield climbs.
- Drying and trim discipline. Test your numbers at a stable 58 to 62 percent relative humidity, trimmed. That is the weight everyone means when they say grams.
How to measure your own number
- Put a wall meter on the fixture circuit and record actual draw, including drivers and any fans sharing that circuit. Ignore the equivalent-wattage claim on the box.
- Weigh trimmed, dried flower once cure weight stabilizes.
- Divide grams by actual watts.
- Also divide by canopy square footage. Together, those two numbers tell you whether the light is weak or the grow is weak.
Common ways the number gets inflated
Marketing watts are the classic one. A fixture advertised as 1000 W that pulls 110 W from the wall will produce g/W figures that mean nothing. Wet weight is another, since fresh flower can weigh four times what dry flower does. And many posted yields quietly include trim, larf, and popcorn buds that never reach a jar.
One more: comparing a room with eight weeks of veg against a commercial flip-at-three-weeks run. The long veg room will post fewer grams per kWh and often fewer grams per watt, while producing more total flower. Both numbers matter, just not for the same decision.
Targets to write down
- First LED grow, average canopy: 0.5 to 0.8 g/W.
- Competent home grower, dialed canopy: 1.0 to 1.3 g/W.
- Strong home or small commercial room: 1.4 to 1.8 g/W.
- Sealed, CO2 enriched, high-efficacy fixtures, experienced crew: 2.0 g/W and up, occasionally.
If you hit 1.0 g/W with real dry weight and true wall draw, you are doing fine. The next ten percent comes from canopy uniformity, not from buying more watts.