I use one to two pea sized ... Servings? I'm not sure what you call a single brushing session worth of toothpaste. Serving feels wrong, and so does dose, portions or squeeze.

I use one to two pea sized dollops of toothpaste two to three times a day. I know I should use a bit less but I can't be bothered to not overshoot a little, and too little toothpaste feels like garbage.
Depending on what I eat for lunch and if I'm home I'll brush after lunch.

I'm willing to bet the biggest difference in duration of tubes is the brand. I know some of the specialty toothpaste tubes are literally a quarter the size of my standard issue toothpaste.