Sized Nappies
From CntWiki
There are 2 sorts of Nappy Sizing options when you are buying - Birth-to-Potty Nappies and sized nappies.
Sized nappies are generally available in small, medium and large. This varies from brand to brand and some brands may have many more than 3 sizes which could include premmie, newborn, extra-small, toddler, large toddler etc.
The advantage that sized nappies have over Birth-to-Potty Nappies is that they tend to give an excellent fit at all times as you change the size of nappy used as your baby grows, much as you do with their clothes. This means less bulk when then are small and a good fit even for a late training toddler, or an older child that needs nappies at night still. The disadvantage is that over the whole period of nappy use it may work out more expensive than using Birth-to-Potty Nappies, although you can sell on each size as you go on various websites (including the Cloth Nappy Tree Classifieds ) which helps spread the cost.
Often people presume that they will need to buy every size of any particular brand which is not always the case due to crossover in the sizes. As an example I moved my child out of his small sized nappies at around 7 months and he fitted into a medium Fuzzi Bunz at that point - he was still wearing those same medium Fuzzi Bunz when he was dry at night at 3.5 years.