1. Check Your Baby's Weight: Weight is the most accurate indicator to ensure a snug and secure fit around the neck and armholes.
2. Measure Total Length: Measure your baby from the top of their head to the bottom of their heels while they are lying flat.
3. Allow Room for Hip Movement: Ensure the sleep sack provides ample space at the bottom for natural leg movement and healthy hip development.

Safety Note: Always choose a sleep sack based on your baby’s current weight and height. Never buy a larger size for them to "grow into"—a sleep sack that is too big around the neck can cause your baby to slip inside, which poses a safety risk.