You can take cologne on a plane following TSA's liquid rules:

• Carry-on luggage: Each cologne or perfume bottle must be 3.4 ounces (100 milliliters) or less and fit inside a single quart-sized, clear, resealable plastic bag along with your other liquids, gels, and aerosols

• Checked luggage: You can pack larger bottles of cologne or perfume, up to 17 ounces (500 milliliters) per container, in your checked baggage without restrictions on quantity, as long as the bottle has a lid to prevent leakage

• Number of bottles: There is no official limit on the number of cologne bottles you can bring, provided each is within the size limits and the total liquid volume in your carry-on does not exceed 68 ounces (2 liters)

• Additional tips: If your cologne bottle is larger than 3.4 ounces and you want to carry it in your carry-on, you can transfer some into a travel-sized container of 3.4 ounces or less

• International flights: Regulations may vary by country, so check specific airline or destination rules, but the TSA 3-1-1 rule generally applies for liquids in carry-ons

In summary, for carry-on bags, cologne must be in containers of 3.4 ounces (100 ml) or less inside a quart-sized bag, while larger bottles can go in checked luggage without size restrictions up to 17 ounces per bottle