I've seen single-file Fortran code that exceeds 15k lines of code, and I have no doubt that there exist source files orders of magnitude larger than that. Belo

I've seen single-file Fortran code that exceeds 15k lines of code, and I have no doubt that there exist source files orders of magnitude larger than that. Below 1000 lines, it depends on the style. If those are all a single function, then you're up a creek. If those are neatly split into many independent functions, then it can be pretty manageable.