how much salmon to purchase for 10 guests

I'd err towards 5 lbs. - accounts for any unusable bits of a whole fish, plus I prefer having a bit too much than too little - I find it makes serving a 'communal' fish a little more relaxed. (With a filet pre-cut into individual portions, or salmon steaks, I'll be more precise and figure 6-8 oz/person.) Also, as Greenstuff said, leftover salmon is a great reward the next day.

I'd also get 4 or maybe even 5 pounds, depending, of course, on how much else you're serving. When it comes to salmon, I always try to have leftovers and all-too-seldom actually get them.

I always plan on 6 ounces of fish per serving for a main course. I would probably buy 4 pounds, because should an extra guest materialize, you could wangle an extra serving .

3 pounds should be sufficient as I assume you'll also be serving sides?? Yum!

Make sure all of your guests like salmon. I've been invited to dinner twice with salmon being served, and it's one of the few things I can't even force myself to eat.

I recommend between 6-8 ounces per person for an entree, 2-3 ounces per for a plated appetizer. 6 ounces works out to about 0.4 lbs, so you can do the math easily when you go shopping.