You can carry liquids on a plane in containers of 3.4 ounces (100 milliliters) or less per item when in your carry-on baggage. All these containers must fit within a single, transparent, resealable plastic bag that holds no more than 1 liter (about 20cm x 20cm in size). You are limited to one such plastic bag per passenger

. This rule applies to liquids, aerosols, gels, creams, pastes, and similar substances, including drinks, toiletries, and cosmetics. Liquids in containers larger than 100ml generally cannot be taken through security in hand luggage, even if partially full, unless they fall under specific exemptions such as essential medications, baby food, or liquids bought at duty-free shops sealed in security bags

. Some airports, especially in the UK and Ireland, have started to relax these rules, extending the liquid limit to 2 liters in some cases, but this is not yet universal and depends on the airport

. In checked baggage, there are usually no specific volume restrictions for liquids, but weight and size limits for baggage still apply

Summary:

• Maximum container size: 100 ml (3.4 ounces) for carry-on liquids.
• All containers must fit in one transparent resealable bag of max 1 liter.
• One bag per passenger.
• Larger quantities allowed in checked baggage.
• Exemptions exist for medications, baby food, and duty-free liquids.

This is the standard rule in the US, UK, EU, Japan, and many other countries