at all times text encoded in UTF-8 will never give us more than a +50% file size of the same text encoded in UTF-16. true / false?

Question

Somewhere I read (rephrased):

If we compare a UTF-8 encoded file VS a UTF-16 encoded file, At some times, the UTF-8 file may give a 50% to 100% larger fil

Answer 1

Yes, you are correct. Code points in the range U+0800..U+FFFF gives a +50% size.

                   UTF-8   UTF-16
U+0000..U+007F       1        2
U+0080..U+07FF       2        2
U+0800..U+FFFF       3        2
U+010000..U+10FFFF   4        4