The problem with GitLab's calculator is that it's simply... too ambitious. They try to calculate the salary for pretty much every somewhat major city in the world and it's simply impossible. You can't capture the details of so many different local economies.
For example, when I lived in England, the difference between rent for a room in a shared house outside city center and a 1 bedroom apartment in the city center was usually at most 100% (excluding the very top and very bottom of the ranges). Meanwhile in Lithuania, where I live at the moment, the difference is about 6 times. You can't capture this in a calculator with such broad coverage.
For example, when I lived in England, the difference between rent for a room in a shared house outside city center and a 1 bedroom apartment in the city center was usually at most 100% (excluding the very top and very bottom of the ranges). Meanwhile in Lithuania, where I live at the moment, the difference is about 6 times. You can't capture this in a calculator with such broad coverage.
Approach by mozilla (https://news.ycombinator.com/item?id=13881004) seems much more reasonable to me, to be honest.