Need some quick advice!

For a 6 Gal. batch with OG @ 1.080 should I use 2 packs of Nottingham or is one OK?

http://www.mrmalty.com says you'll need 2.8 packs so I'd throw them both.

Use 2 if you got em. Otherwise pitch one and you can add on later when you can get to the LHBS. But you know what? 1 pack will be just fine. There are many LHBS and online stores making a lot of money on yeast sales. So its in their best interest to scare you into buying "the correct amount" of yeast. Pitch rate calculators are good for determining the optimal amount of yeast, but we as homebrewers really don't need that kind of precision.

Funny thing about yeast is that it will multiply and eat as long as there is food present. Some argue that under-pitching can cause off flavors due to stressing the yeast, but in a 1.080OG beer, I am not sure you will notice those flavors anyway.

Coming soon: Myth busters - Homebrewing edition

I'm getting 16 g dry yeast, assuming 100% viability, using Mr. Malty. Depending on the age of the yeast, likely there would be no harm in using 2 packs. Make sure to re-hydrate.

Thanks guys, I put both in after hydrating.

With all due respects to Mr. Malty, I think it over estimates the amount of yeast needed. What does it use to determine what the correct pitching amount is.

I'm not advocating grossly under pitching, but it seems that there is an optimum level of under-pitching that brings out the best in the yeast. I have read a number of reports from brewery's that deliberately underpitch to bring out more yeast character in their beers, I think 'Farmhouse Ales' also advocates under-pitching.

However; I think a single pack of Notty in a 1.080 is pushing it, but you should be OK. There are a couple of problems with severely under-pitching: Stressing yeast and a stuck ferment, and creation of fusel alcohols.

Adding a second pack a couple of days into the brew is not going to do much. he reproduction phase is over.