I have been having issues with my measurements and it got me thinking if I'm kegging 5 gallons and I have some head space, then what is the exact volume of the keg?
Good question, I've had a couple batches that filled my 5 gal carboy to about an inch below the mouth, there still seemed to be an inch and a half of head space in the keg from them. You could get a gallon milk jug, and see how many it takes to fill to the top. I've never worried about it, or I would have done that myself.
The corneys that I have state the capacity is below 5 gal. 4.5 or something. I assume this is for the soda and they leave space in them, but I have not measures them yet.
I have a semi-related post in "talk me down". Based on that experience, I would say that a 5 gallon carboy filled to the top would equal my soda keg filled to the top.
I had saved gyle for carbonation - a little over 2 pints. This didn't look like it would fit in my carboy before racking and it didn't all fit in my keg after racking.
JMass, what kind of "soda keg" do you have? Mine are the standard ball-lock kegs that Pepsi retired. I also have a couple pin-locks from Coke, but I haven't used them so I have no idea what they would hold. The Coke kegs are a little shorter and wider than the Pepsi ones, so maybe they have less capacity.