Thanks for asking, Angie! For a measurement of 5.25", you should select the Extra Small (XS) size for the Medline Wrist and Forearm Splint.
Sizing Breakdown
Extra Small: Generally covers wrist circumferences of 5.25" and under.
Small: Typically begins at 5.5" to 6.25".
Why Fit Matters
Compression: A proper fit ensures the compression is distributed evenly across your wrist and lower forearm.
Thumb Position: Since this model features an abducted thumb (spica), the XS will ensure the thumb stirrup aligns correctly with your smaller frame rather than sitting too high or loose.
Thanks,
The Medical Supply Pros Team.