First Time Washing Yeast - need help estimating yeast quantity

I washed a yeast cake for the first time this morning. Pictures are attached. The first one is immediately after pouring the slurry into the jars and the second is about 25 minutes later. I decanted the top two layers into 4 pint sized jars. What's a good estimate for the yeast quantity that I've collected?

Beer info:
Yeast cake from a 5 gallon batch of Centennial Blonde
The beer was in primary for 10 days
A dry packet of Safale S-04 was used to ferment

I think you can estimate the number of cells in the yeast cake and then do some math to determine the number in a pint. How much guesswork is involved?

I would also like to know the best way to estimate. Generally, I have read that it should be measured by weight, but there seem to be a lot a variables with that method.

My guess is the that you have a metric crap load of yeast in both containers.

I found a good article on Wyeast's website that I'm going to use. I'll post again when I've made a starter with some of this yeast.

http://www.wyeastlab.com/com-yeast-harvest.cfm

Not scientific, but I use about 1"-2" from my spaghetti sauce jar when I pitch.

There is also some very good reading at the yeastcalc site. http://yeastcalc.com/
I use this site for my starters and only this site, as it seems to be spot on and up to date.

Using consistent pitch rates is important to getting consistent results. I have tried the same recipe with the same yeast at different pitch rates...you would swear they were two different beers. So, get one of those syringes with the "ml" reading from your local pharmacy.
I have read there could be anywhere from 1 to 5 billion yeast cells per ml of slurry. I use the figure of "2 billion per ml"...and it seems to work out nicely.

Now that you are washing, move on to freezing your yeasties too. The freeze dried kind are the best to play with since they are cheaper than the premium strains. I freeze my yeast in these 8 dram bottles from Amazon
http://www.amazon.com/dp/B002JVDN5C/?tag=skimlinks_replacement-20
They hold 29 ml of fluid. I fill mine with 14 ml yeast(I figure 28 billion cells) slurry before I freeze. I personally figure 33% survive the freeze/thaw process, giving me 9.3 billion healthy yeast to put in my starter. More than enough, as I have read of some people that do slanting, only freeze a few MILLION cells, and still get good results.

Generally, 1-2 billion cells per ml. If you are using it soon, go with 2B. If it's going to sit in the fridge for a while, go with 1B. Unfortunately, unless you have lab equipment, it's tough to know.