Once you've decided to cloth diaper and selected the cloth diapering system you are going to use, your next step is to determine the proper size for your baby.
Although most manufacturers and/or WAHM-made cloth diapers and diaper covers will give a suggested range using baby's age and weight for sizing, the absolute best gauge of whether a diaper will/will not fit a child is to offer waist, thigh and rise measurements. Knowing your baby's waist, thigh, and rise measurements will not only help you select diapers, but ensure that once you do choose a diaper size, you are less likely to have messy leg and waist leaks, and protect baby from a fit that is uncomfortably tight.
How to measure the waist, thigh and rise on a baby.
First, start with measuring at the waist. Obviously, a baby is not going to have an hourglass figure that makes it easy to select and measure the waistline. Whether baby is plump with rolls or long and lean, you'll always measure in the same place - all the way around, level with the belly button. If you are measuring for a cloth diaper, you need to measure the baby without any other diapers on. If you are measuring for a cloth diaper cover, you will need to measure baby over the style of cloth diapers he or she will wear under the diaper cover.
Next, measure your baby's thighs. When measuring your baby's thighs, measure around the fullest part of baby's upper thighs and be sure to measure against baby's bare skin. Even just 1/4 of an inch difference can make a difference between baby's poop staying in the diaper or on your hip! This is NOT the area where the leg meets the lower torso - that will always be smaller ... it is a bit further down the thigh - where it begins to round out. Again, measure around the fullest part.
Finally, you need to know your baby's rise measurements. The rise, sometimes called the "depth" is the length from your baby's belly button (at the waist), between their legs, and back up to the same place (at the waist) on their backside. If you are measuring for cloth diapers, you need to measure on bare skin. If you are measuring for cloth diaper covers, you need to measure baby over the style of diaper you will be using with that particular cover
These three measurements will allow you to select a cloth diaper and cloth diaper cover with the most accuracy in fit for your baby. If you purchase from an online cloth diaper store that does not offer measurement guidelines for waist, thigh and rise, it is wise to ask the store owner BEFORE making your purchase.