Short answer
Indoors, expect roughly 100–500 g of dry flower per m² (about 10–50 g, 0.3–1.6 oz, per ft²), rising with canopy light. Well-run research rooms reached 500–750 g/m². Worked back from the trials, that's about 0.7–2 g per watt of efficient LED. Supported for the light response; the g/W range is our arithmetic.
Why
Yield follows light. Dry flower rose linearly from 116 g/m² at 120 µmol/m²/s to 519 g/m² at 1,800 µmol/m²/s [1], and a second trial found the same proportional response [3]. Another group measured 500–750 g/m² at 750–900 µmol/m²/s and 0.22–0.36 g per mole of photons [2].
Watts become photons through efficacy. Good LEDs exceed 2.5–3 µmol/J [4]. At 2.5 µmol/J, an average 900 µmol/m²/s needs about 360 W per m² of fixture, if the light lands on the canopy.
So g/W is a ratio of two numbers you can estimate. At about 300 g/m² under 450 W/m² (a less efficient fixture), you get ~0.7 g/W. At 720 g/m² under 360 W/m², ~2 g/W. Tent walls and edges waste some light, so home tents sit lower.
The numbers
| Canopy light (µmol/m²/s) | Dry yield, g/m² | g/ft² | 2 x 2 ft tent | 4 x 4 ft tent |
|---|---|---|---|---|
| ~120 (weak) | ~115 | ~11 | ~40 g | ~165 g |
| ~600 | ~230 | ~21 | ~80 g | ~330 g |
| ~900 | ~300 | ~28 | ~110 g | ~430 g |
| 750–900, dialled in [2] | 500–750 | 46–70 | 180–270 g | 720–1,080 g |
| ~1,800 (very high) | ~520 | ~48 | ~185 g | ~750 g |
Rows 1–3 and 5 interpolate the linear response in [1]; cultivars differ.
What to do
- Use g/m² to compare grows; quote g/W only with the fixture's wall watts.
- Measure average PPFD across the canopy, not the centre point.
- Raise light gradually towards 800–1,200 µmol/m²/s in flower.
- Buy efficacy (µmol/J), not "equivalent watts".
Common mistakes
- Using a fixture's marketed "equivalent" wattage.
- Comparing g/W across different run lengths.
- Chasing g/W with light the plants can't use without CO₂.
- Expecting more light to raise THC: it raises grams, not potency [1].
Related
- Full article: PPFD and DLI by stage
- Answers: yield per plant · what wattage for my tent · increasing yield
- Terms: grams per watt · photon efficacy · yield
