2923.11 Definitions.
Text of Statute
As used in sections 2923.11 to 2923.24 of the Revised Code:
(A) "Deadly weapon" means any instrument, device, or thing capable of inflicting death, and designed or specially adapted for use as a weapon, or possessed, carried, or used as a weapon.
(J) "Ballistic knife" means a knife with a detachable blade that is propelled by a spring-operated mechanism
K) "Dangerous ordnance" means any of the following, except as provided in division (L) of this section:
(1) Any automatic or sawed-off firearm, zip-gun, or ballistic knife;
2923.12 Carrying concealed weapons.
Text of Statute
(A) No person shall knowingly carry or have, concealed on his or her person or concealed ready at hand, any deadly weapon or dangerous ordnance.
2923.17 Unlawful possession of dangerous ordnance; illegally manufacturing or processing explosives.
Text of Statute
(A) No person shall knowingly acquire, have, carry, or use any dangerous ordnance.
Ohio law does not specify any blade length as legal or illegal, and as you can see the definition of "weapon" is very broad. The only specifically prohibited knife type is the ballistic knife. However, many cities and villages do limit blade lengths in their local ordinances. Typically these prohibit the carrying of any knife with a blade length greater than 2 1/2 inches.