2 1/2 gallon batches and yeast

I'm about to brew up a few 2 1/2 gallon batches and was wondering if using one whole pack (be it a smackpack or a white labs liquid vile) is too much yeast for this batch size or would it be fine? Also, If i were to brew 2 small batches this size and share a pack of yeast between them would that be enough yeast?

Most 5 gallon beers really need more than a smack pack or vial of yeast. You'd be doing yourself a favor to use a whole one in 2.5 gallons. If you share a pack, you'll still get beer, but I've found that pitching lots of yeast is one of the best things you can do to assure a healthy fermentation and a good beer.

It's not too much yeast for 2.5 gallon batch. Some people pitch twice the recommended amount of yeast in their brew. I do it.

And after one batch, you could reuse the yeast cake.

I do 2.5 gallons and use 1 vial/smack pack per batch. Works great.

Check this link out... It will tell you how much yeast to pitch based on the viability of your smack pack. http://www.mrmalty.com/calc/calc.html

I brew 2.5 gallon batches and was surprised to learn that sometimes, one smack pack isn't enough...

Doesn't it depend on your SG, and what kind of beer or cider you 're making? I just put together a cider with a SG of 1.090 and used a packet of Red Star Montrachet. I'm thinking it may not have been enough, and this is a 2.5 gallon batch. The way i understood yeast and sugar is that the more sugar you have, the more yeast you need to attenuate it down. A 1.040 beer wouldn't need as much yeast as a 1.090, or maybe not necessarily NEED it, but be able to use it. I brewed a 1.100 belgian quad, used a smack pack that I made a starter out of, and pitched a WLP500, just to be safe. It's been 25 hours, and the things been going crazy. blowing off kreusen, and bubbling up like a machine gun. I added the extra yeast because I raised the SG and didn't want to get stuck with a batch of beer that wasn't fully fermented. I'm only on my 4th batch of beer and first of cider, so maybe I'm not so well informed on the activity of yeast, but this is how I thought it worked