You only need to squeeze out an amount the size of a pea on to the bristles of your toothbrush.
The image of squeezing along the entire length of the brush bristles was concocted by an ad agency, a la Mad Men, to make consumers use their toothpaste faster, hence buy more product.
I've never used that much. I just assumed it was to look nice since a pea sized about would look silly in a picture. I think it I used that much my mouth would be so full of foam it would be uncomfortable
I swear it's also why they made that newer garbage cap design that slowly leaks toothpaste and gums up unless you carefully clean the end and fully close it every time. I know y'all know what I am talking about!
in fairness the directions on the back of the tube still state you should use a pea sized amount. i feel like that's not all that helpful though, peas come in lots of different sizes.