I am asking this question because for some reason ascii codes from range 128 - 255 have a size of 2 bytes but their composition is 8 bits which makes them a "byte". So I am confused as to why this certain ranges have 2 bytes when all of them only consist of 8 bits for example :

127 → 01111111 (1 byte)

>>> len(chr(127).encode('utf-8'))

255 → 11111111 (2 bytes)

>>> len(chr(255).encode('utf-8'))
  • $\begingroup$ What do you mean by a "size of 2 bytes"? Python-specific questions are off-topic here. $\endgroup$
    – D.W.
    Aug 17, 2022 at 16:27
  • 1
    $\begingroup$ Codes 128-255 are extended ASCII. But UTF-8 is not ASCII. $\endgroup$
    – user16034
    Aug 17, 2022 at 18:31

1 Answer 1


A "byte", as defined by the C and C++ standard, is the accessible unit of memory, and exactly large enough to hold one char, signed char, or unsigned char. It must be at least 8 bits, but can be larger.

A "byte" that is exactly 8 bits in size is also called an "octet". Octets are always 8 bit, bytes are not.

Ascii-codes from 128 to 255 don't exist. ASCII only has code points from 0 to 127. Unicode code points range from 0 to 0x10ffff. Unicode code points from 0 to 127 have a one-to-one mapping to ASCII-codes. Unicode code points from 0x80 to 0x7ff use two bytes in UTF-8 encoding; code points from 0x800 to 0xffff use three bytes, and code points from 0x10000 to 0x10ffff use four bytes.

UTF-8 is an encoding of code points, other encodings are UTF-16LE and UTF-16BE, and UTF-32LE and UTF-32BE. An encoding has different properties from the unencoded values. There are many other encodings for subsets of Unicode, but they are falling out of fashion.


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