At U.S. TSA checkpoints, liquids, aerosols, gels, creams, and pastes in carry-on bags must follow the 3-1-1 rule: each container may hold no more than 3.4 ounces (100 milliliters), and all of those containers must fit in one clear, quart-sized bag per passenger. Containers larger than 3.4 ounces belong in checked baggage, even if they are mostly empty.
Medications and infant or child nourishments are exempted from the size limit but still go through screening. Duty-free liquids over 3.4 ounces bought on inbound international itineraries may be allowed in a secure tamper-evident bag with the receipt when TSA’s conditions are met.
Source: Transportation Security Administration — Liquids, Aerosols, and Gels Rule.
Image: Airport liquids packing poster; David Lisbona, CC BY 2.0, via Wikimedia Commons.