The Allbirds Tree family and the Wool family fit differently given their material makeups. The Tree shoes are made from lyocell (commonly referred to as "Tencel"), while the Wool shoes are made from merino wool.
Wool will naturally stretch over time, while the Tree retains shape. If you're normally a full size, we suggest sticking with that size in all styles :)
If you typically wear a half size, we suggest sizing up in our Wool Collection. For the Tree, we've found that most half sized customers size down in the Tree Runners and up in the Tree Skippers, Loungers and Toppers. Please note that we now do include half sizes in our Tree Breezers! We recommend sticking with your true size for that particular style. If you have a wider foot, we'd suggest going up to the next full size in each silhouette.