When you want to get detailed about gpw, especially when testing against what everyone else says won't work, try this formula:
https://www.rollitup.org/t/proper-calculation-of-gram-per-watt-ratio.843161/
I'm not saying its the de-facto, but it takes into consideration all costs.
Out of curiosity,
@Sativied, woud you agree?
IMHO, if you can prove out this formula with 1kW against 2kW in a 5x5' space, I'd really like to know about it.
-spek
I recently read a story about how Jorge Cervantes supposedly made up gpw after traveling the world and comparing different growers results. Nothing saying I believe it, not even sure it was serious, but interesting nonetheless, and the supposed reasoning does align with how I'm used to using gpw and seeing it being used for decades. Which is to compare yields in rather standardized hps setups.
Veg time is irrelevant as it depends on plant count. Flower time is irrelevant (for gpw) because it differs per strain. It's based on 400/600w on 1 square meter which is 3.28x3.28 feet. When I say 3x3, 4x4, or 5x5 in these forums, I really mean 1m2, 1.44m2 (120cm x120cm) or 150x150cm (2.25m2) which does skew the numbers a little, but, 1 meter closet isn't always exactly 1 meter either. In other words, space is rather irrelevant too. If you want to use 1m2 or 3x3 feet or 4x4 even for 600 watt that's up to you. The determining factor will still be the light.
It sure is nice to know the flower duration and obviously the amount of cycles per year matters when you're growing commercially, but those variate a lot amongst growers. In the end, all that matters when it comes to gpw is gram and watt. The whole reason for the desire to add more variables is because the increasing amount of different grow setups. Adding more factors and variables doesn't make it more useful though, on the contrary. It's the simplicity that gives or at least gave it some value when comparing.
A common saying amongst dutch growers is "Light is weight" (it rhymes in dutch). Obviously only true to a limited extend, but the w in gpw is* a steady and common factor (amount of light is limited to space, although that's supposedly debatable according to this thread) so that's what we compare yield to.
*I should say 'was' with all the different settings even on hps, different bulbs, and LED.
All that said, that doesn't mean your formula isn't useful, but honestly no I can't say I agree. Is it a better way to calculate
cost? Yes, obviously. Although when you get to the point that matters (the cost of vegging and other equipment) it's more about yield per cycle in total and then there are additional costs such as space and labor costs. Is it a better way to compare
yields? No, imo it's not for the reasons above. To put it differently, your formula is more suitable for reducing costs, gpw is simply to gauge if you're getting a certain amount from a given setup, it doesn't serve well as an accurate measurement in a competition.
