The lovely topic of soft structured carriers (SSCs). Many people find them incredibly comfortable due to the padded straps and waist. The issue is that there are very few that are suited for newborns. And as your baby grows, the support needed will change and vary.
In our local lending library, I have gathered many SSCs for members to try, but often get asked which is needed for a certain age/weight of baby or which will last the longest. Let me say this: many babies are the same size but different weights. Many babies are the same weight but different age. It's time to let go of our fascination with the weight. To properly fit your child to a SSC, you will need to go off pant size. It's the support from knee to knee that is the determining factor.
Here's a list of SSCs that I have personally measured. The measurements are of the base, where the carrier would support baby's bottom and knee to knee. You will see they all vary. I will add more as I receive/measure them. I hope this clears the air a bit and helps you find the best fit for your baby!
Babyhawk Mei Tai - 15.75"
Babyhawk Oh Mei - 15.25"
Babyhawk Oh Snap - 15.75"
Beco Gemini - 6.25" snapped down. 12" fully open.
Beco Soleil - 16"
Boba - 14"
Emeibaby - adjustable from 6" on up
Ergo Original - 14.5"
Ergo Sport - 14"
Fidellal Fusion - adjustable from 6" to 19"
Infantino Union - 14.5"
Kinderpack Infant - 7.5" fully cinched. 16.25 fully open.
Kinderpack Standard - 18"
Kinderpack Toddler - 20"
Kinderpack Pre-school - 22"
Lenny Lamb Baby - 14"
Lenny Lamb Toddler - 15" narrowest. 17" widest.
Lillebaby - 6" snapped down. 16" fully open.
MO+M - 12.5"
Olives & Applesauce - 15"
Onya Baby - 16"
Tula Standard - 15.5"
Tula Toddler - 19.25"