Baby clothing sizes are typically broken down based on averages, and because babies grow at different rates, not all babies of the same age will fit into the same size clothing. However, here are some general guidelines for baby clothing sizes by weight:

• Preemie: Up to 5 pounds
• Newborn: 5 to 8 pounds
• 0-3 months: 8 to 12 pounds
• 3-6 months: 12 to 17 pounds
• 6-9 months: 17 to 21 pounds
• 9-12 months: 21 to 25 pounds
• 12-18 months: 25 to 28 pounds
• 18-24 months: 28 to 30 pounds

Its important to note that these sizes represent an average range, and the size listed will be the upper limit of that range. So, if you have a 3-month-old, they will likely be ready to graduate from 0-3 month sizes into 3-6 month sizes if they havent already. When in doubt, its best to size up, as babies grow fast and pants and sleeves can be rolled up if an item is too big for your little one.