S size: inner diameter 15CM (suitable for 3-12 months, 10-20 catties) L size: inner diameter 16CM (suitable for 6-30 months and 16-30 catties) XL size: inner diameter 19CM (suitable for 2-4 years old, 25-44 catties) Design - Our baby swimming buoy provides the ideal swimming position for babies, making it easy for babies to learn to kick and swim in a horizontal position instead of a vertical position. Raised front and widened sides: prevent flipping, and soft bottom support keeps baby from sliding out. Portable - Easy to inflate and deflate. Out of the box portability and storage. The new version of the Perfect Travel Pool Float - Great for swimming pools, tubs, beaches, Note - 1. Each product is gas tested. Be careful not to inflate too much (80%-90% inflation is enough) 2. Warm reminder: The size after inflation is affected by saturation and material elasticity, and there will be a 1-3 cm error