How do I adjust the Ergobaby Omni Classic carrier seat to my baby's size?

Use the seat adjustment tabs on the inside of the waistband to narrow or widen the seat based on your baby’s height. For babies 20–24 in/50.8–61 cm (~0–3 months), follow the red line indicators; 24–28 in/61–71 cm (~3–9 months), yellow line; and over 28 in/71 cm (~9 months+), blue line. Please use caution as the numerical guidelines above may not match true sizing exactly. The intent is to make sure that the width fills out to the napes of baby's knees.