I have made a one liter starter with one vial of wyeast activator at 1.04 gravity. I figure that gives me about 200billion cells now, right? I need to get to 500billion cells. I have a 4L flask. Can I take the 200 billion cells and get to 500billion in one go or do I need to split it up?
another 2L or so should get you in ballpark on a stir plate. i’d do a bigger first step next time- 1L is the smallest recommended. figure roughly 1gal starter for what you are targeting.
You can chill decant and add back about a liter and a half of wort at 1.030 or so and you should be pretty good to go. That is rough horseback estimate based on doing the Mr Malty online calculator many times but not being at my computer presently (just an iPad) - you can push it to 2 liters and run the calculation to zero in on it, then save any excess!