Bottling and Kegging - how much sugar

[erf]

Tomorrow is the big day - I am spicing my Christmas brew - it has been in the FV for a fortnight and tomorrow it gets kegged and bottled. I have 20 650ml Fisher bottles and a 5 gallon keg for the rest. The big question is how much sugar do I need to prime what goes into the keg? I'm assuming I need more than normal because the keg will be less than half full, so I need it to produce a lot more gas to achieve the same pressure (and therefore the same level of carbonation). Any suggestions on how to calculate this? Total brewlength is 23 litres.

Also, I'm planning to make a tea for my spices - how does this sound for a recipe?
3 tsp cinammon, 1 tsp nutmeg, 1tsp cloves, zest of 3 oranges, 2cm fresh ginger all boiled in a pint of water.

[floydmeddler]

Probably a bit late but I use this:

http://hbd.org/cgi-bin/recipator/recipa ... ation.html

I go for 1.35 volumes of carbonation. This gives me just enough fizz to create a nice fluffy head, just like a casked ale