How much yeast for 2.5 gal batch?

[Ryan11]

Since I can just split my 5 gal recipe in half....can I use half a white labs vial of yeast or should I use the whole thing?

 

[jonny_crash]

http://www.mrmalty.com/calc/calc.html

 

[shawnbou]

Use this:

http://www.mrmalty.com/calc/calc.html

A vial of liquid yeast should really be propagated into a starter before you pitch to a full volume batch of wort. A vial on its own is not really enough for a 5-gallon batch, so half a vial is not going to be enough for 2.5 gallons.

If you can't make a starter, I'd just pitch the entire vial.