In most states, the legal length for a pocket knife is less than 3 inches, generally 2 1/2 inches. Laws regarding knives vary depending on the state; however, longer knives are legal in all states as long as the knife is noticeably intended for utility use.
Carrying certain knives, such as switchblades and butterfly knives, is illegal, as these knives are considered concealed weapons. These types of knives have a blade noticeably longer than 3.5 inches. There are also specific places where carrying a knife is prohibited, such as inside courthouses, schools, planes and federal buildings. When considering carrying a pocket knife, it is best to research the laws for the applicable state.