That's per square metre.
12 oz in a square metre is very nice, high five.
It all depends on your technique, and how much light you are throwing at it.
I aim in a SOG to get about 1/2-3/4 ounce per plant flowered at ~5" as a rooted clone.
If all you care about is weight, run a commercial strain like Big Bud, M39, Mighty Mite, Northern Lights, or Papaya.
Xcrispi gets over a pound a plant indoors. But he is vegging a very very long time, which takes a high level of skills to not kill the plant.

Do not count the chickens before the eggs are even laid.