To clarify and expand upon my prior comment in light of Nanci's recommendation, my small fuzzies are generally 4 to 6 grams and regular fuzzies are 7 to 9 grams, and then that can vary by supplier. I can imagine that there are things labeled as fuzzies in the chain stores that are barely more than large pinkies. I weigh my mice and I've have had pinkies that are a little larger than some of my smallest fuzzies. The difference is seen mostly in the amount of fur and the tail length.
If you want to feed 7 gram fuzzies to a 30 gram snake that has been eating 3 gram fuzzies, I recommend moving up in size gradually. Slitting can help, as Nanci said (and I do note she has far more experience than I, and I have the utmost respect for her recommendations).
My snake weighs 41 grams, is gaining 3 grams a feeding on a 6 day interval and is still on 5.5 gram fuzzies. That's based on the bulge the mouse makes, the speed at which she digests it, the weight gain I measure, and her shape (the so called loaf of bread cross section -- an underfed snake will have a triangular cross section). I have a lot of fuzzies to choose from and will gradually be moving her up in size after she sheds. She's currently in blue and I skipped her scheduled feeding last night.
I am purposely feeding more conservatively than the Munson Plan. After a lot of reading and study here and other places, I believe that it is best for the long term health and longevity of my snake. How agressively to feed a growing youngster is a decision each snake owner has the responsibility to make for themselves. By telling you what I'm doing, I'm giving input; and certainly only you can decide, within reason, the exact details of how to feed your snake.