well for folding knifes if you hide it the blade must be under 3in but you can carry what ever you want as long as every one can see it.it is all up too you if you are doing bad things the people will be all like he has a knife he is dangeris so dont brake the law in front of the mormens or thay will call the cops
EDIT:The quote above is crap. Don't bother trying to make sense of it.
See Utah Code 76-10-504 and 76-10-501 and you'll see the knife laws you're looking for. Any knife regardless of size is considered a dangerous weapon based on...
(i) the character of the instrument, object, or thing;
(ii) the character of the wound produced, if any;
(iii) the manner in which the instrument, object, or thing was used; and
(iv) the other lawful purposes for which the instrument, object, or thing may be used.
If, based on these criteria, your knife is deemed a "dangerous weapon" in a court of law then you must have a concealed carry permit or it's a Class A Misdemeanor.
Go here for confirmation:
http://le.utah.gov/dtForms/code.html
Search for the words "knife" and "concealed carry" and you'll find the above. There is also a definition of "knife" under 17-50-332 stating ""knife" means a cutting instrument that includes a sharpened or pointed blade." Not that you needed Utah to tell you that.