Grams per watt is a yield efficiency figure: dry grams harvested divided by the wattage the lights draw. A 480 W light producing 480 g is "1 g/W". It is popular because it is easy to calculate, but it mixes two things: how efficient the light fixture is and how well the grower uses the light.
In practice
Home growers commonly report around 0.5-1.0 g/Wbeing reviewed; efficient LED rooms with good genetics and environment report more. Be careful comparing numbers: use wall wattage, not the "equivalent" wattage marketed on fixtures, and state the run time, since a longer flower adds weight.
A more physical measure is grams per mole of photons (g/mol), which removes fixture efficiency from the equation. Research shows yield rises with photon delivery, and that fixture efficacy (µmol/J) matters more to cost than fine spectrum tweaks.
Units and formula
g/W = dry flower (g) / fixture power draw (W). Example: 600 g / 720 W = 0.83 g/W.
Don't confuse with
- g/m²: yield per area; the better comparison between grows.
- Photon efficacy (µmol/J): a property of the light, not the grow.
