depends on how old the vial is. I prefer to try to double my growth each step, or 50 to 75 mill/ml (innoculation rate).
example: I brew 12 G batchs, so if my viability of a vial is 70%, that is 70 bill cells instead of 100 bill cells per vial.
I split the vial up front and do two starters simultaneously, effectively putting 35 bill cells per starter. I will make 2x .5L , decant, and make 2x .8L starter for brew day. I would not see much more growth if I made the first step 1L vs a 2L. which is why you want to keep an eye on the innoculation rate. You end up saving DME or starter wort compared to what you would go through otherwise