Depends somewhat on the variety. Sprouting varieties generate multiple shoots and more seeds. I would guess 0ne- two ounces per plant

I let some Brussels sprouts go to seed this year from overwintering, and I got at least ten thousand (10,000) from each plant, though I did not save all of them.

I now have hundreds of Brussels sprouts seedlings coming up where the plants were.

I also let a few broccoli plants flower, but they were regular types and they didn't flower as vigorously as the Brussels sprouts. Only a few of the flower buds opened.

I don't know how the Brussels sprouts seedlings would taste as sprouts like broccoli, but you could have my seeds if you wanted them. They are not much use in growing because I let hybrid and open pollinated plants flower at the same time and didn't isolate them. I don't have room or time to see how these plants will do.

If sprouting broccoli produces many more sprouts, it looks like you would want to raise that kind.

Last year I let some hybrid broccoli go to seed and the volunteers made a very thick green crop that fall. So a good side sprouting variety like Castle Dome or Emerald Crown would produce hundreds or perhaps thousands of seed apiece.

Average per plant is about 6,000 (4,300 to 9,300) seeds. You will want to save from at least six for diversity.

Depending on the size of the seeds, 10,000 14,000 per ounce.