Sizing:
 
To determine the appropriate sandal size, measure your foot from toe to heel.  Select the sandal that is the same or slightly larger.  These are flip-flops and do not require an exact fit.

For Her (white):
 

Small Medium Large

9"   from heel to toe  10" from heel to toe 11" from heel to toe

For Him (black):
 

Medium Large X-Large

11" from heel to toe  12" from heel to toe 13" from heel to toe