What size of knife are you allowed to carry?

Knife size limits depend on location, law, and knife type. In the US, many places allow ordinary folding knives with blades around 3 inches or less without much scrutiny, but that is not a universal rule. Some states focus on concealed carry, some regulate automatic or fixed-blade knives, and some restrict knives only in schools, courthouses, airports, or government buildings. Cities can also impose stricter local rules than the state. A legal blade in one county can still create a problem in another. The practical rule is simple: blade length, opening mechanism, carry method, and restricted locations all matter, and local law controls the answer.