It's difficult to give a definitive answer on the maximum size knife you can carry, as it varies depending on the airline and country you are travelling to and from. TSA used to allows knives with blades that are 2.36 inches (6 cm) or less in length in carry-on.

In 2026, transportation security regulations (such as those from the TSA in the U.S.) strictly prohibit all knives with blades of any length in carry-on luggage. While some international aviation authorities have historically experimented with allowing very small blades (under 6cm), the standard for major global travel remains a "zero-tolerance" policy for blades in the cabin to ensure passenger safety. This restriction includes pocket knives, Swiss Army knives, box cutters, and even tactical multi-tools. If you need to travel with a knife, it must be packed in your checked baggage and securely sheathed or wrapped to prevent injury to baggage handlers. Plastic or round-bladed butter knives are generally the only exceptions, though security officers always have final discretion at the checkpoint.