If you are curious to know how much toothpaste you can bring on a plane then the rule of TSA 3-1-1 answers your question. Airlines allow up to 3.4 ounces of liquid and gels in any form, it can be in the form of water, juices, toothpaste, shampoos, hair conditioners, hair gels, etc. Any amount exceeding this limit will be charged extra. There is an exception for medications to this rule, if you have prescribed medications in liquid form, you can take them as much as you want.