I just checked Corrine Netzer's "Complete Book of Food Counts", 2000 edition, and it lists (specifically Quaker) unprocessed bran as having 11 gm carbs and 8 gm fiber in 1/3 cup. Hmmm......... For just generic plain old bran, it lists 2 Tbsp (which is 1/8 cup) as 4.5 gm carbs and 3 gm fiber. That's the count I've always gone by.
I'd play it safe rather than sorry, and use the higher count. Besides 1/2 cup is a lot of bran to eat at one sitting, remember that it SWELLS. Don't want to end up with a tummy ache!!

A lot of lowcarbers take sugar-free Metamucil or use the plain psyllium husks as a source of extremely low-carb fiber... .. I use ground flax seeds and a little wheat bran, as I am severely allergic to psyllium.

hope this helps

Doreen