For the uninitiated, here is a primer on disposable diapers.

Don't load up on newborn size. You can plan on using plenty of diapers for your newborn, but unless you’re the parent of multiples, it’s overkill to buy economy packs, which may contain up to 160 newborn diapers. Your baby is likely to outgrow the newborn size before you use that many. In fact, some babies are too big at birth to ever wear the smallest size. Buy by your baby’s weight. Start with one package of 40-count newborn diapers if your baby weighs less than 8 pounds at birth. If your baby weighs 8 pounds or more, start with a package of size 1s, then buy in volume after you find the brand you like best. Don’t be afraid to experiment. You’ll find a favorite brand in time.

Bigger is better. In general, purchasing the largest-count package you can find is the way to go. Opting for an extra-large case of Pampers Baby Dry, for example, rather than the jumbo-size package, could save you up to 9 cents per diaper, depending on the size of the diaper you buy. You’ll save the most money if you buy store-brand diapers in economy-size boxes, which come in counts that range from 92 to 252; you can also find competitive deals on name-brand diapers on sale, in packages of various sizes.

Don’t be too quick to jump to the next size diaper. Selecting the smallest diaper your baby can wear comfortably will save you money in the long run because a larger diaper costs more. Manufacturers usually charge the same amount per package regardless of the actual size of the diapers, but they will put progressively fewer diapers in the package as the size gets larger. In addition, a diaper that is too roomy may allow leaks.

Diaper sizes vary from brand to brand. One brand’s size 1 may fit children from 8 to 14 pounds, while another’s fits those from 8 to 18 pounds, combining sizes 1 and 2 into one package. A brand’s weight ranges usually overlap: Size 2 in one brand covers 12 to 18 pounds; size 3, 16 to 28 pounds; and so forth.

Get more valuable baby shopping information in the Consumer Reports Best Baby Products guide, available in bookstores nationwide.