While there are numerous types and brands of diapers from which you can, using the right-sized diaper is key to keeping your baby comfortable and preventing leaks. Most kids begin potty training by the age of 2, notes MayoClinic.com, but that doesn’t mean your child won’t use diapers longer. As your baby grows, you'll need to purchase larger-sized diapers so they continue to fit comfortably and work properly. There are several ways to determine when it's time to go to the next size in diapers.
Know your baby's weight. Most diaper manufacturers size diapers based on a baby's weight. Knowing your baby's exact weight can let you know if she’s outgrown her current diaper size and is ready to move up a size. Your doctor can let you know how much your baby weighs when you take her for checkups. Alternatively, you can purchase your own baby scale. You can also weigh yourself on an adult scale and then weigh yourself while holding your baby. The difference in the two weights will let you know how much your baby weighs.
Check the fit of the diaper. If the diaper fits like a "bikini" or pulls to one side, it's likely the wrong size -- and it's time to move up to the next size. A diaper should be straight and symmetrical. The waistband should fall right at the waist — not too high in front or too low in back or vice versa, notes the Huggies website.
Inspect your baby’s waist and legs. Look for signs her current diaper is too tight, such as red marks or rashes around the legs and waist where the diaper is too tight against the skin. Even if your baby's weight is appropriate for the size diaper you are using, if the diaper is irritating your baby's skin, it might be time to move up to the next size.
Pay attention to how well the diaper is working. If you notice the diaper is leaking through to your baby's clothes each time it’s wet, it’s likely that the diaper is too small and you need the next size diaper. While you can expect occasional leaks, a diaper that is too small will produce more frequent leaks.