I am planning a 5 week trip to an area of the world that
- is very sunny
- does not have the same stores, nor the same selection in stores, as we have where I live
I use sunscreen that is 85 SPF, 110 SPF if I can get it. 60 generally isn't good enough for my needs if I'm going to be outside all day. Feel free to do the math and tell me that I don't need it; you're wrong. I have in the past got a sunburn from being outside 15 hours with SPF 40 meticulously re-applied frequently. I've had this skin over 50 years, I know how it reacts to sun, and only the development of these super high SPFs has freed me from constant hat and shirt wearing.
This sunscreen is reasonably hard to find here at home. I tend to buy 2 and 3 tubes at a time when I see it. I'm going to assume it will be impossible to find on the trip. I just used up a tube of it in the Bahamas and that made me realize I will probably need to take multiple tubes with me on the long trip. But how can I know how much to take?
I suppose this boils down to "how much sunscreen does a person use in one full application?" but some heuristics around multipliers on that (not every day needs full applications, right?) would be super helpful. I'm trying to travel light, so taking 10 tubes of sunscreen and bringing 7 of them back home with me would be suboptimal.