Under the global 3-1-1 liquids rule, you can take shampoo in your hand luggage as long as the container is 3.4 ounces (100 milliliters) or smaller. It is a common mistake to assume that a half-empty 6-ounce bottle is acceptable; security officials strictly look at the label capacity of the bottle, not the amount of liquid inside. All your 100ml containers must fit comfortably inside a single, clear, quart-sized (1 liter) resealable plastic bag. In 2026, while some major airports are installing advanced CT scanners that theoretically allow for larger liquids, the 100ml limit remains the legal standard at the vast majority of international checkpoints to ensure a consistent security protocol. If you require more shampoo for a long trip, the best peer-to-peer advice is to pack full-sized bottles in your checked baggage or switch to solid shampoo bars, which are exempt from liquid restrictions and save significant space in your toiletry kit.