I am always uneasy at the idea of carrying around a fixed blade. For this reason, my backpack knife is a multitool (A fantastic Leatherman Blast, which saved the day already many times). I would like to know where I can find information and procedures to safely carry around a knife (if at all) when it comes to fixed blade, but also more in general for any kind of knife.
I carry a fixed blade knife almost every day and it has a 4.5 inch blade (the Cold Steel Roachbelly, if you were wondering), and nobody has stopped me for it. I'm not sure what the legal length for a fixed blade is, though. I know that for a folding it's 3.5",but I don't know what it is for fixed.It might also be 3.5", but I don't know.
Laws vary greatly by region, and are subject to being changed at any time. That being said, there are a few sites I used when looking up the knife laws in California.
http://en.wikipedia.org/wiki/Knife_legislation Provides a good overview of knife laws, but did not provide the specifics I need. It's worth browsing the sources that they reference however.
http://knife-expert.com/sta-law.htm Seems to have a good summary of knife laws for each state.
http://thefiringline.com/library/blades/knifelaws.html Very high level overview of state knife laws in a table, showing the concealed vs open carry status.
I wouldn't take any of these as fact, just as guidelines or resources to help you locate your official state / region's laws regarding knife laws.