It depends on your estimated cell count. What was the manufacture date on the yeast pack? Use a little yeast calculator like this:
http://www.cheapmonkeys.com/yeastcalc/ to help you work out how "viable" your pack is, and therefore what size starter you'll need to get to your required cell count.
Check this image out:
https://drive.google.com/file/d/0B9zdUs ... sp=sharingI've put in a 19l batch of 1.049 ale. It tells me you "optimally" need 173 billion cells to pitch liquid yeast. Then I've put in that you had a Wyeast pack manufactured on April 1, 2014. That tells me you have 46 billion viable cells in that pack (they drop from 100b pretty quick).
So in 1st step, I've put in a .5 litre starter, and chosen "Stir Plate" as the method of aeration. As you can see, it says you'll end up with 108 billion cells. Which is still 65 billion short of what you need for an optimal pitch rate.
If you do a 2nd step, another 500ml starter into which you pitch your 108b will result in 172b, so that would work. Of course your pack might have been newer than April 1, which changes things a bit?
Next time...a 1.5 litre starter would have given you 180b cells, which would have worked. You'll need a bigger flask though, unless you do what I do and use a 3 or 4l plastic bottle, and just shake it every now and then (there's a choice for "intermittent shaking" instead of "stir plate".