Having done some searching and reading and checking with some online calculators it seems 1 CSR cube = 1 teaspoon of sugar, and thats about the right amount per 750 ml bottle.
28 (# of bottles) x 4.5g (size of sugar cube) = 126 grams.
Is this correct, or will I end up with either bottle bombs (well, a mess and split PET bottles) or flat beer?
edit. Next time I will prob. bulk prime, or the time after (will use up the cubes first) but not this time as can't find any food grade hosing locally unless I buy 10 meters of the stuff. Will have a look on the site sponsor's sites for what I need.