how much yeast from washing?

I have a stout in the primary right now fermenting with WLP001. Part of the reason for this batch was to build up a good bit of yeast for a barleywine that I'm planning on doing next week. I know in theory I could just pitch onto the cake, but since it was a stout I figured it would be better to wash the yeast so I won't have to worry about the previous batch affecting the flavor of the barleywine. The part I'm not clear on is how to determine how much yeast I'm actually pitching. I was planning on pitching however many jars of yeast I need to in order to get an appropriate pitching rate, so is there a correlation like 1 quart jar = 1 vial of yeast or something that I should go by? Am I better off just pitching directly on the cake from the previous batch?

If you're going to go the cake route, i think data suggests to remove *some* of the cake prior to pitching. The whole cake would be too much. Though, in the past i've used full cakes which have turned out fine. If you DO wash, you'd be best served to utilize a starter and step up a few times for the cell count to be plenty for a BW.

Regarding the equivalents (1 jar = 1 smack pack, etc.), i can't comment on that, as i just deal in increments of starters in quarts.

The age of the yeast slury, thickness and purity are all factors in deciding how much to pitch. Use the calculator on mrmalty.com to help figure it all out. http://www.mrmalty.com/calc/calc.html

A 1.050 beer will need 86 ml of yeast slurry. That would be less than 1/10 of a quart jar.

That number is good if you are washing the yeast.

Or just using a portion of the cake? If so, I would double or triple it.