Hi nannoo,
It's difficult to be exact because we all metabolise carbs differently, we all produce differing amounts of insulin in response to the carbs in our diets and we all expend energy differently. It is reckoned that we each need a minimum of 50 grams of carb per day in order to meet an average day's energy requirements. Some people find that they cannot process even that amount of carbs and opt for one of the low-carb diets, like Atkins, Bernstein, South Beach, typically around 30g carb per day. (The shortfall in carbs is made up by the body by burning off fat in order to keep energy levels up.) Others find that they can eat a higher amount of carbs and still maintain good control (I have on average 100-120g per day and my BS readings are consistently 6 to 6.5 on the mornings and 4.5 to 5.5 in the evening). Some people are happy on 80g, some on 180g.
Some rely on a low GI diet. This is effectively a form of carb reduction because practically everything at the low end of the GI tables contains far less carbs that foods at the upper end of the GI table. We all differ and what works for one will not necessarily be the best thing for another. You need to experiment to find what works for you and what to avoid. And if, like me, you enjoy your food, it can be good fun experimenting!
One of the hardest things that us regulars on here have to do is try to convince someone that they must ignore the dietary advice given by their doctors, because what is a "healthy" diet for a non-diabetic is usually an extremely unhealthy diet for a diabetic. We have all been there, followed the doc's advice as laid out in that nice NHS healthy eating brochure (see note below), got the t-shirt and in some cases got the diabetic complications. We have found the hard way that the official guidance is wrong.
* Note: the NHS leaflet is very generously printed on behalf of the NHS . . . . by the world's largest manufacturer of insulin! So guess who'se interests are served by getting people to eat as many carbs as possible!!