Yep, what Nova and Maxs said. I thought you were wondering about number of seeds to plant to reach your "desired goal." Like I said in my post: '80-90% germination; but only 2 of 3 to reach transplant.'
After plant pokes its little head up, you still might get some of this:
seed cap stuck, dampening off, over-fert, under-lit, over-water, dried out, weak plants / runts, insects / pests / varmints, pets, children, adults, dropped, stepped-on, too much wind, rain, heat, cold, ghouse structure failure, stolen, vacation, stunting, root bound, root rot, fungus, lawn mower, sunburn, waste (too many of wrong type plant, not sold or planted).
Here's a link with a few observations about numbers of seeds to get your grow on:
germination poll
Alabama Jack also had a great score sheet on his grow last year which really nails down a lot of variables involved in a big grow also, beyond germination rate.