Natural Priming Calc. for Kegging?

[FB12]

I know this has been discussed before, so sorry if redundant, but how do you know how much corn sugar to use for natural priming a keg? I've read 1/2 cup & 1/3 cup, but have'nt found a real measureable amount depending on style as i used for bottling. Is this just a "rule of thumb" or is there a calculator available? I'm kegging my first batch tomorrow, and haven't finished my keezer yet. I figure natural priming will give me a few weeks to finish building. Also, after sealing with CO2 and checking for leaks, do you purge a couple times before setting in closet for 3 weeks? Thanks for help!

 

[tektonjp]

I use the same calc as for bottles. I could never understand all the fuss about "smaller headspace" needing less sugar. I haven't had any problem with what I would consider over varbonation.
Sealing with CO2 and purging is usually done together, or in my mind, the same thing.
Good Luck.