Measuring Yeast

So I have properly rinsed my yeast and it is sitting at the bottom of my mason jar which has water to the top.

How do I measure it? I have been to Jamil's calculator, however I dont know what tools or steps to take to go from here.

For pitching from slurry he gives you the amount in mL. I use a Nalgene bottle that has mL marked instead of a mason jar. But with your mason jar, you will just need to do the volume calculation of your jar and then convert to mL.

Ahh, i see it on the side now. I have 100ml of yeast. Now if I need 100 there would be no need for a starter right? How many cells would there be if I made a starter and then pitched?

I don't usually use a starter because I am brewing back to back and the viability hasn't dropped too much. You need to make sure you put in your harvest date so you can calculate the viability.
You can use the Liquid yeast tab of Jamil's calculator for calculating cell count after a starter. The number of cells produced depend on your aeration method and volume of starter. Play around with the calculator and it should start making sense.

If you go to the bottom of the Wyeast page here

http://www.wyeastlab.com/hb_pitchrates.cfm

There is a good graphic on how you can estimate the number of cells in your slurry. you can do this with a 50ml tube, by mixing up your slurry and filling the tube with 50ml of the slurry, then letting it settle.

also you can weigh the yeast suspension to get an estimate of the total yeast in solution. but I don't have the numbers here with me, but if someone has access to the Yeast book, they might post it here for you.

Okay I looked it up, each Yeast weighs ~8x10^-11 Grams so 100 billion yeast will weigh 8 grams. Water weighs 1 gram per 1 milliliter, so if you weigh 100ml of your slurry and it weighs 108 grams you have 100 billion yeast in your suspension or 1 billion yeast/ml.You can do a little math and make a simple formula

((weight in Grams of 100ml of slurry)-100g)*(100 billion yeast/8g)=total yeast in 100ml of slurry.

Depending on how well you rinsed your yeast you might want to adjust this number down but 10-15% to account for non yeast solids in the slurry.

Hope that helps.