Over Yeasting?

I have a package of Liquid Yeast. The whole package is meant for a 5 Gallon batch but i'm brewing on the 2 gallon scale...

use the whole package? measure out half?

any advice would be great.

Liquid yeasts meant for five gallons don't actually have a high enough cell count for five gallons; just pitch the whole pack.

Yes, just pitch the whole pack.

Like the others said, liquid yeast only have sufficient cell count for beers up to approximately an og of 1.030. So you're underpitching for most beers if you don't make a starter.

The Mr Malty pitch rate calculator is the best tool to use to determine the right amount of yeast for your job, EVEN in a 2.5 gallon batch of beer.

Even in a 2.5 gallon batch if your gravity is around 1.080, mr malty begins to suggest using a starter for a single package of liquid yeast/. It's not a lot at that point, but the calculator begins to start showing your short of cells....

So if your gravity's no more than 1.080 you should be alright with just the single tube.