<<Disclaimer: Verify this information before applying it to your situation.>>

Sorry I can't give you an exact number, but the glycemic index helps
answer this question. Some carbs seem to pack more of a punch bg-wise
than others.
For instance I can eat broccoli with no problem, but rice is
troublesome.

One of the other pieces of this dietary puzzle is finding out which
carbs YOU can handle.
You just have to do a lot of self-testing to see what foods work for
you.

~fran