also with mr malty, it will give me a viability of my yeast based on the date of harvest, and the amount of yeast I need based on o.g., but I don't see a formula for determining how much yeast I currently have, like I said before maybe I just don't understand that calculator
MrMalty is intended to tell you how much slurry to pitch based on the volume and specific gravity of the wort you're pitching into and the conditions of your slurry (slurry density and % non yeast). However, you can use it indirectly to determine how much yeast you have.
So let's make some assumptions. First, let's assume you have 1.8 billion cells per mL and 10% non yeast particulates in the thick cake at the bottom. We would use 4.5 billion for the 140 mL, but since you have 210 mL total solution, you have ~67% yeast slurry This means you need to set the yeast concentration to 1.8 billion/mL and the non yeast to 10%. I arrived at the 1.8 billion/mL by extrapolating the data listed on Wyeast's site that I linked.
Now all you need to do is change the volume of wort you're pitching into until the yeast slurry converges to your actual slurry (210 mL in this situation). The standard setup into 5.25 US gallons of 1.048 wort lists 177 billion total cells and 112 mL of our slurry (1.8 billion/mL and 10% non-yeast). Increase the volume of the wort until it arrives at 210 mL slurry. I will save you the trouble, 9.8 gallons of 1.048 SG wort requires 330 billion cells. This is equivalent to 210 mL of yeast slurry from our specific slurry parameters (1.8 billion/mL and 10% non yeast).
This requires a few steps, but there's a much easier way to arrive at the same answer. Multiple the 1.8 billion/ml by the amount of slurry you pitch. As Wyeast mentions on their site, "Harvested slurry is typically in the 40% to 60% solids range. A home brewer can make a rough estimation based on this information and combined with consideration for all other factors involved (trub content, age of yeast, strain, original gravity, etc.)."
For a 55% slurry, you have 1.4 billion/mL. Extrapolating for a 67% (140 mL yeast/210 ml total volume), gives ~ 1.8 billion cells/mL. Then all you have to do is multiple 210 mL by the slurry density, and you will arrive at 378 billion cells. You can also add a non-yeast correction factor to account for all the settle particulates to not be yeast, just assume a 10/20% number and then multiple your volume of yeast by 90%/80%. From there, you can calculate the percent yeast solids and use the Wyeast site to calculate slurry density.
From that analysis, you probably have around 330 - 380 billion healthy yeast cells in the 210 mL of solution, just call it 350 billion. I would just mix the 210 mL solution and then pitch the appropriate volume to get your proper pitch rate. For instance, if you wanted to pitch 250 billion cells, just take 250 billion cells divided by 350 cells per 210 mL. This means you'd need to pitch 150 mL of a well-mixed slurry to the wort to arrive at 250 billion cells.