I actually measured my K2 capacity with a ratio-rite, but I forget for sure.

2.5 quarts to the top mark of the dipstick comes to mind. i remember it was less that i thought, I thought it would be closer to 3 in the tank.
That means the lines, sump and filter must hold another quart.
Sorry, but this post subscribes me to the thread. My tank is still off, if i get a chance I'll measure it again.