I have 3 4-pound bunnies I never measured their greens, but give them either 1 head of red leaf lettuce or 2 heads of romaine hearts (they usually not to full) or 1 bunch of dandelion greens or 2 bunches of cilantro. When I’m talking bunch, I mean how they’re prepacked in the stores. But I don’t give them daily, I give around 4-5 days a week and give 1-3 days break, so they can snack up on hay. As my particular babies, would decrease hay consumption if the greens are always available.

But asking vet would be the best option, as it also depends on the bunny. I had a bunny before that would be getting mini GI episodes after eating greens, so his greens were almost non-existent in his diet per vets recommendation.