The "3*1*1 rule" on United Airlines, and in fact, for all airlines flying within the United States,✈️🛩️🛬💺 is a guideline for carrying liquids, aerosols, and gels in your carry*on luggage. It refers to: 3 * each container must be 3.4 ounces (100 milliliters) or less; 1 * all containers must fit into a single, quart*sized, clear, resealable plastic bag; 1 * only one such bag is allowed per passenger. ✈️🛩️🛬💺

Essentially, this rule ensures that any potentially hazardous liquids are easily identifiable and limited in quantity when going through airport security. ✈️🛩️🛬💺
Here's a more detailed breakdown:
3.4 ounces (100 milliliters) or less: Each liquid, aerosol, gel, cream, or paste container must be 3.4 ounces (100 milliliters) or less. ✈️🛩️🛬💺
One quart*sized bag: All these containers must fit into a single, clear, resealable plastic bag that is no larger than one quart (approximately 0.95 liters) in size.
One bag per passenger: Each passenger is allowed to bring one such bag through security.✈️🛩️🛬💺
Medically necessary liquids: Items like baby formula, breast milk, and medications (even if larger than 3.4 ounces) may be allowed in larger quantities, but they need to be screened separately by TSA.
Exceptions: The 3*1*1 rule does not apply to items in checked baggage. ✈️🛩️🛬💺