There is no recommended size for anything that may harm another person. All weapons must not be taken onto any public transport including an airplane.
There is no length limit for a pocket knife in Hawaii.
4 inches
12 Inches...
6 inches
Any fixed blade knife is legal. The law for a folding "pocket knife" no blade longer than 3" can be concealed. Therefore it is legal to own any knife although you can not conceal (hide on your person) any non-fixed blade over 3".
A standard pocket knife or folding knife no longer than 4.5 inches in the closed position is legal to carry. I believe daggers, bowie, spring loaded or butterfly knives are not legal to carry.
4 inches
In louisiana you can carry a machete and it's legal
In California, it is generally illegal to carry a concealed switchblade or knife with a blade longer than 2.5 inches in public places. However, it is legal to carry a folding pocket knife with a blade shorter than 2.5 inches. It is important to note that individual cities and towns may have their own specific regulations, so it is advisable to check local laws before carrying any type of knife.
States have different age limits. It is not legal to carry them in school.
Unable to answer without more information. WHAT kind of "pocket knife?" Some are specifically declared illegal by statute. And were you doing anyting with it besides just innocently carrying it in your pocket . . where no one could see it?
Of course not! People carry pocket knives a lot. Why shouldn't they be able to carry around steak knives, butter knives, butcher knives, or penknives?