How much yeast from yeast cake

Ok so I am going to harvest yeast from my yeast cake for the next batch I do. I've looked into all the different calculations for making a starter and the amount of cells and all that. My question is when you harvest yeast from a yeast cake how do you know ROUGHLY how many cells you have and what size starter you need to make?

From everything I have read you can look at yeastcalc.com or mr.malty under "slurry" and it should give approx. amount in mL. for a repitch. Personally I believe there are huge variances with repitching from a slurry (cake or whatever you want to call it). I tend to just take a 1 cup scoop from the cake and dump it in the next batch. I only do this for beers where overpitching is not a concern (i.e. APA, IPA). If you have a beer that gets flavor from yeast (i.e. Belgians) then I think it is better to get your mL slurry closer in line to what the yeast calcs call for.

1 "scoop" haha I love it. The more I learn about brewing the more I am intrigued but also the more worrisome I become lol

1/4 to 1/2 cup of slurry is enough for beers 1.070 and smaller.