First of all unless you are using a light mover 12 plants under 1 1000w light is to many... I usually Start with 8-10 under one light because 1 or 2 plants always seem to have a problem so I wind up with 6-7 healthy plants... a 1000w light is good for a 4x4 space and you should only have 1 plant per square foot which is 8 max... If you try to grow to many in that area all your plants will suffer for it..
Second there are to many variables to tell you what you should get... If you are a first time grower you will be lucky to get .5 grams per watt of light...
yep one 1000wtt light is not enough light unless they are only going to be a foot or two tall and then still really the buds won't be a t there full potental because of lack of lumans.. but you do it.
Did EITHER of you read his post? He vegged for 50 days. Its obvious that they will be over a foot tall, mygirls, and biggun your advice is just stupid. You tell him that 12 plants is too many? Why? Since he's vegging for 50 days, he'll have gigantic plants for sure. In fact, 50 day veg time is probably 2x too long.
But regardless, 12 plants is not too many for a single 1kW lamp, it's more than YOUR PREFERENCE.
And dont be a prick and insult the kid with 0.5g/watt. Any idiot with a light can get that.
So, original poster, here's the ACTUAL ANSWER to your question. Your yield from a single 1000w lamp is generally about 2 Lbs per harvest. Sometimes lower, 1.5 Lbs or sometimes higher, 2.25Lbs max for me. Each strain yields differently.
It isnt about how many plants you have under a light, its about making sure the top canopy of plants is non stop green for the entire square. That's it!
I wish I could -rep people for some of their stupid advice they post just for trying to get +rep wrongly.