Sizing for function

The function of what you are designing could go a long way to determining the size. This is particularly true if you are combining your print with another part. If I had a lobster claw clasp I wanted to use with a custom designed pendant, I would want to make sure the hook for that pendant was wide enough for the clasp. Once that is decided, aesthetics may kick in. I may size the rest of the piece purely to look proportionate with the hook.

Existing objects also give good direction with sizing. Making a coaster? Measure a coaster you already have. Holiday ornaments, paperweights, bottle openers, magnets, soap dishes, earrings, bookmarks, and business card holders are just the tip of the iceberg. Your house and your office are full of reference objects to guide you with sizing.