While your rabbit is pregnant, unless she seems to be becoming thin, don't feed her any more than a non-pregnant rabbit. The amount you feed depends on her size, condition, and the type of feed. If she is larger than around six pounds, I would feed her 3/4 to 1 cup of feed per day. If she weighs less than about six pounds, I would feed her 1/2 cup of feed per day. You don't generally need to worry about the weight in ounces of the feed. Just start out with a certain amount and pay attention to her body condition. A protruding backbone or easy-to-feel boniness would mean she needs more to eat. If, however, she seems to become too fat (developing lots of folds of skin or a backbone that can't be felt), reduce her feed. A fat doe will have a harder time kindling.
Once she kindles, though, begin free feeding her, as she'll need more calories to produce plenty of milk.