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Why did UTF-8 replace ASCII?​ Key Reasons Behind the Encoding Change

The ASCII encoding system was fundamental in the early days of computing languages and protocols. However, it is only able to characterize 128 code points, and has been mostly suitable for the English language. That's why ASCII was replaced by the famous UTF-8, a Unicode-based encoding system that can represent 1,112,064 characters, making it useful to encode words with accents, non-Latin terms, and emojis.

Stay with us along with this article, where we will understand the features of UTF-8 and ASCII, approaching the following subjects:

  • What is the ASCII code?
  • What is UTF-8? Why did UTF-8 replace ASCII?
  • UTF-8 vs. ASCII — an example.
  • Is ASCII an extension of UTF-8?
  • How can I convert UTF-8 to ASCII?
  • Should I use UTF-8 instead of ASCII?
  • And much more.

But, if you want to encode any message in ASCII, you need to check our fantastic ASCII converter.

Firstly, let's provide a brief description of the ASCII code. ASCII is an acronym for American Standard Code for Information Interchange. ASCII is a character encoding standard representing a set of 128 code points. In a simple way, the ASCII code maps different characters to numbers, allowing computers to store and transmit text. You can see the charts of characters in ASCII in detail by accessing our ASCII converter.

This code was developed in the 60s by Hugh McGregor Ross and Robert William Bemer, and it was known in Europe as the Bemer–Ross Code. A problem with the ASCII code is that it was created to be functional in the English language. Therefore, the necessity of having such a mechanism work in other languages and to type emojis led to ASCII being replaced by an 8-bit system, also known as UTF-8.

Despite its simplicity, the ASCII code has historic relevance in the development of protocols and programming languages. We can mention, for instance, that ASCII is the base for programming language syntax, email headers, HTTP, and HTML.

As we saw in the previous section, the ASCII code was not enough to describe all the characters of different languages. In order to overcome such an issue, the UTF-8 (Unicode Transformation Format – 8-bit), was developed in 1992 by Ken Thompson and Rob Pike. This encoding system can represent 1,112,064 characters (also known as Unicode characters), and has a one-to-one correspondence with ASCII. This design means that a pure ASCII text still works in UTF-8.

Each character of UTF-8 can be encoded as 1 to 4 bytes, as presented in the table below:

First code point

Last code point

Byte 1

Byte 2

Byte 3

Byte 4

U+0000

U+007F

0yyyzzzz

U+0080

U+07FF

110xxxyy

10yyzzzz

U+0800

U+FFFF

1110wwww

10xxxxyy

10yyzzzz

U+010000

U+10FFFF

11110uvv

10vvwwww

10xxxxyy

10yyzzzz

where the letters u to z represent the different code points and blue indicates an unused byte.

All these features made UTF-8 become the standard encoding mechanism in electronic communication. Since 2025, almost all webpages are based on UTF-8. Moreover, UTF-8 has been applied in all modern operating systems and programming languages.

Let's create an example to illustrate the correspondence between UTF-8 and ASCII. Suppose that you want to encode the word Omni in ASCII and in UTF-8. By following the codes of an ASCII chart and the UTF-8 table, we can verify that:

Character

UTF-8 code point

ASCII (decimal)

ASCII (hex)

UTF-8 (hex)

O

U+004F

79

4F

4F

m

U+006D

109

6D

6D

n

U+006E

110

6E

6E

i

U+0069

105

69

69

As we can see, the UTF-8 code points have the same hexadecimal representation in both ASCII and UTF-8, revealing the correspondence between these encoding methods. Feel free to check the ASCII hexadecimal representation of this word with our ASCII converter.

🙋 Would you like to write messages with different encoders? Then, access our Morse code calculator and Vigenère cipher calculator.

No, it is precisely the other way around. UTF-8 can be considered an extension of ASCII. In fact, UTF-8 was developed to embed ASCII, making previously created ASCII texts compatible with it. The code points U+0000 – U+007F use exactly the same single-byte values as ASCII. Moreover, ASCII encodes 128 characters, while UTF-8 can represent more than 1 million characters.

Since ASCII just works well in the English language, you can only convert words without accents, non-Latin scripts, or emojis. Otherwise, you need to adapt your text by removing these special characters. Let's make an example with the word code:

  1. Take the UTF-8 code points for code:

    c = U+0063; o = U+006F; d = U+0064; e = U+0065

  2. Take the hexadecimal correspondence for these codes in UTF-8:

    c = 63; o = 6F; d = 64; e = 65

  3. Take the decimal correspondence in ASCII:

    c = 99; o = 111; d = 100; e = 101

Yes, you should choose UTF-8 instead of ASCII. ASCII is embedded in UTF-8; therefore, your text or algorithm will be compatible with both codes. Moreover, the ASCII is limited to encoding 128 characters. So, it will not work well with accents, non-Latin terms, or emojis. However, UTF-8 is the most widely used encoding method in HTML, operating systems such as Linux and macOS, and programming languages like Python 3.

This article was written by João Rafael Lucio dos Santos and reviewed by Steven Wooding.