In the NaturaLash Online Eyelash Extension Certification course we have a whole section devoted to selecting the proper eyelash extension shapes and sizes that are right for your client.  

In general, the 8-12mm eyelash extensions are the most popular lengths, with the majority of 9-11mm's being used (typically 8 or smaller are used on the inner lashes and 10 or longer are used on the outer lashes).  Applying 50-100 eyelash extensions per eye of these sizes is generally a great way to create a look that almost every client will love.  The key here, however, is applying a full set.  Anything less than 30-50 lashes per eye is usually not considered a full set and can result in a less full look and typically need a touch up much faster.  

What are your favorite sizes or eyelash extensions?  Ultimately it is up to you as a professional to do a consultation with your client to determine what look they are going after and what sizes you think will best achieve that look.  If you have any questions about this please feel free to reach out to us or signup for our 3 day online eyelash extension certification course!  Happy lashing!