What is the difference between UTF-8 and Unicode?

To expand on the answers others have given:

We've got lots of languages with lots of characters that computers should ideally display. Unicode assigns each character a unique number, or code point.

Computers deal with such numbers as bytes... skipping a bit of history here and ignoring memory addressing issues, 8-bit computers would treat an 8-bit byte as the largest numerical unit easily represented on the hardware, 16-bit computers would expand that to two bytes, and so forth.

Old character encodings such as ASCII are from the (pre-) 8-bit era, and try to cram the dominant language in computing at the time, i.e. English, into numbers ranging from 0 to 127 (7 bits). With 26 letters in the alphabet, both in capital and non-capital form, numbers and punctuation signs, that worked pretty well. ASCII got extended by an 8th bit for other, non-English languages, but the additional 128 numbers/code points made available by this expansion would be mapped to different characters depending on the language being displayed. The ISO-8859 standards are the most common forms of this mapping; ISO-8859-1 and ISO-8859-15 (also known as ISO-Latin-1, latin1, and yes there are two different versions of the 8859 ISO standard as well).

But that's not enough when you want to represent characters from more than one language, so cramming all available characters into a single byte just won't work.

There are essentially two different types of encodings: one expands the value range by adding more bits. Examples of these encodings would be UCS2 (2 bytes = 16 bits) and UCS4 (4 bytes = 32 bits). They suffer from inherently the same problem as the ASCII and ISO-8859 standards, as their value range is still limited, even if the limit is vastly higher.

The other type of encoding uses a variable number of bytes per character, and the most commonly known encodings for this are the UTF encodings. All UTF encodings work in roughly the same manner: you choose a unit size, which for UTF-8 is 8 bits, for UTF-16 is 16 bits, and for UTF-32 is 32 bits. The standard then defines a few of these bits as flags: if they're set, then the next unit in a sequence of units is to be considered part of the same character. If they're not set, this unit represents one character fully. Thus the most common (English) characters only occupy one byte in UTF-8 (two in UTF-16, 4 in UTF-32), but other language characters can occupy six bytes or more.

Multi-byte encodings (I should say multi-unit after the above explanation) have the advantage that they are relatively space-efficient, but the downside that operations such as finding substrings, comparisons, etc. all have to decode the characters to unicode code points before such operations can be performed (there are some shortcuts, though).

Both the UCS standards and the UTF standards encode the code points as defined in Unicode. In theory, those encodings could be used to encode any number (within the range the encoding supports) - but of course these encodings were made to encode Unicode code points. And that's your relationship between them.

Windows handles so-called "Unicode" strings as UTF-16 strings, while most UNIXes default to UTF-8 these days. Communications protocols such as HTTP tend to work best with UTF-8, as the unit size in UTF-8 is the same as in ASCII, and most such protocols were designed in the ASCII era. On the other hand, UTF-16 gives the best average space/processing performance when representing all living languages.

The Unicode standard defines fewer code points than can be represented in 32 bits. Thus for all practical purposes, UTF-32 and UCS4 became the same encoding, as you're unlikely to have to deal with multi-unit characters in UTF-32.

Hope that fills in some details.

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Let me use an example to illustrate this topic:

A Chinese character:      汉
its Unicode value:        U+6C49
convert 6C49 to binary:   01101100 01001001

Nothing magical so far, it's very simple. Now, let's say we decide to store this character on our hard drive. To do that, we need to store the character in binary format. We can simply store it as is '01101100 01001001'. Done!

But wait a minute, is '01101100 01001001' one character or two characters? You knew this is one character because I told you, but when a computer reads it, it has no idea. So we need some sort of encoding to tell the computer to treat it as one.

This is where the rules of UTF-8 come in: https://www.fileformat.info/info/unicode/utf8.htm

Binary format of bytes in sequence

1st Byte    2nd Byte    3rd Byte    4th Byte    Number of Free Bits   Maximum Expressible Unicode Value
0xxxxxxx                                                7             007F hex (127)
110xxxxx    10xxxxxx                                (5+6)=11          07FF hex (2047)
1110xxxx    10xxxxxx    10xxxxxx                  (4+6+6)=16          FFFF hex (65535)
11110xxx    10xxxxxx    10xxxxxx    10xxxxxx    (3+6+6+6)=21          10FFFF hex (1,114,111)

According to the table above, if we want to store this character using the UTF-8 format, we need to prefix our character with some 'headers'. Our Chinese character is 16 bits long (count the binary value yourself), so we will use the format on row 3 as it provides enough space:

Header  Place holder    Fill in our Binary   Result         
1110    xxxx            0110                 11100110
10      xxxxxx          110001               10110001
10      xxxxxx          001001               10001001

Writing out the result in one line:

11100110 10110001 10001001

This is the UTF-8 binary value of the Chinese character! See for yourself: https://www.fileformat.info/info/unicode/char/6c49/index.htm

Summary

A Chinese character:      汉
its Unicode value:        U+6C49
convert 6C49 to binary:   01101100 01001001
encode 6C49 as UTF-8:     11100110 10110001 10001001

P.S. If you want to learn this topic in Python, click here.

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"Unicode" is unfortunately used in various different ways, depending on the context. Its most correct use (IMO) is as a coded character set - i.e. a set of characters and a mapping between the characters and integer code points representing them.

UTF-8 is a character encoding - a way of converting from sequences of bytes to sequences of characters and vice versa. It covers the whole of the Unicode character set. ASCII is encoded as a single byte per character, and other characters take more bytes depending on their exact code point (up to 4 bytes for all currently defined code points, i.e. up to U-0010FFFF, and indeed 4 bytes could cope with up to U-001FFFFF).

When "Unicode" is used as the name of a character encoding (e.g. as the .NET Encoding.Unicode property) it usually means UTF-16, which encodes most common characters as two bytes. Some platforms (notably .NET and Java) use UTF-16 as their "native" character encoding. This leads to hairy problems if you need to worry about characters which can't be encoded in a single UTF-16 value (they're encoded as "surrogate pairs") - but most developers never worry about this, IME.

Some references on Unicode:

The Unicode consortium web site and in particular the tutorials section

Joel's article

My own article (.NET-oriented)

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They're not the same thing - UTF-8 is a particular way of encoding Unicode.

There are lots of different encodings you can choose from depending on your application and the data you intend to use. The most common are UTF-8, UTF-16 and UTF-32 s far as I know.

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Unicode only define code points, that is, a number which represents a character. How you store these code points in memory depends of the encoding that you are using. UTF-8 is one way of encoding Unicode characters, among many others.

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Unicode is a standard that defines, along with ISO/IEC 10646, Universal Character Set (UCS) which is a superset of all existing characters required to represent practically all known languages.

Unicode assigns a Name and a Number (Character Code, or Code-Point) to each character in its repertoire.

UTF-8 encoding, is a way to represent these characters digitally in computer memory. UTF-8 maps each code-point into a sequence of octets (8-bit bytes)

For e.g.,

UCS Character = Unicode Han Character

UCS code-point = U+24B62

UTF-8 encoding = F0 A4 AD A2 (hex) = 11110000 10100100 10101101 10100010 (bin)

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Unicode is just a standard that defines a character set (UCS) and encodings (UTF) to encode this character set. But in general, Unicode is refered to the character set and not the standard.

Read The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) and Unicode In 5 Minutes.

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UTF-8 is one possible encoding scheme for Unicode text.

Unicode is a broad-scoped standard which defines over 140,000 characters and allocates each a numerical code (a code point). It also defines rules for how to sort this text, normalise it, change its case, and more. A character in Unicode is represented by a code point from zero up to 0x10FFFF inclusive, though some code points are reserved and cannot be used for characters.

There is more than one way that a string of Unicode code points can be encoded into a binary stream. These are called "encodings". The most straightforward encoding is UTF-32, which simply stores each code point as a 32-bit integer, with each being 4 bytes wide. Since code points only go up to 0x10FFFF (requiring 21 bits), this encoding is somewhat wasteful.

UTF-8 is another encoding, and is becoming the de-facto standard, due to a number of advantages over UTF-32 and others. UTF-8 encodes each code point as a sequence of either 1, 2, 3 or 4 byte values. Code points in the ASCII range are encoded as a single byte value, to be compatible with ASCII. Code points outside this range use either 2, 3, or 4 bytes each, depending on what range they are in.

UTF-8 has been designed with these properties in mind:

ASCII characters are encoded exactly as they are in ASCII, such that an ASCII string is also a valid UTF-8 string representing the same characters.

More efficient: Text strings in UTF-8 almost always occupy less space than the same strings in either UTF-32 or UTF-16, with just a few exceptions.

Binary sorting: Sorting UTF-8 strings using a binary sort will still result in all code points being sorted in numerical order.

When a code point uses multiple bytes, none of those bytes contain values in the ASCII range, ensuring that no part of them could be mistaken for an ASCII character. This is also a security feature.

UTF-8 can be easily validated, and distinguished from other character encodings by a validator. Text in other 8-bit or multi-byte encodings will very rarely also validate as UTF-8 due to the very specific structure of UTF-8.

Random access: At any point in a UTF-8 string it is possible to tell if the byte at that position is the first byte of a character or not, and to find the start of the next or current character, without needing to scan forwards or backwards more than 3 bytes or to know how far into the string we started reading from.

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The existing answers already explain a lot of details, but here's a very short answer with the most direct explanation and example.

Unicode is the standard that maps characters to codepoints. Each character has a unique codepoint (identification number), which is a number like 9731.

UTF-8 is an the encoding of the codepoints.
In order to store all characters on disk (in a file), UTF-8 splits characters into up to 4 octets (8-bit sequences) - bytes. UTF-8 is one of several encodings (methods of representing data). For example, in Unicode, the (decimal) codepoint 9731 represents a snowman (☃), which consists of 3 bytes in UTF-8: E2 98 83

Here's a sorted list with some random examples.

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1. Unicode

There're lots of characters around the world,like "$,&,h,a,t,?,张,1,=,+...".

Then there comes an organization who's dedicated to these characters,

They made a standard called "Unicode".

The standard is like follows:

create a form in which each position is called "code point",or"code position".

The whole positions are from U+0000 to U+10FFFF;

Up until now,some positions are filled with characters,and other positions are saved or empty.

For example,the position "U+0024" is filled with the character "$".

PS:Of course there's another organization called ISO maintaining another standard --"ISO 10646"，nearly the same.

2. UTF-8

As above,U+0024 is just a position,so we can't save "U+0024" in computer for the character "$".

There must be an encoding method.

Then there come encoding methods,such as UTF-8,UTF-16,UTF-32,UCS-2....

Under UTF-8,the code point "U+0024" is encoded into 00100100.

00100100 is the value we save in computer for "$".

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If I may summarise what I gathered from this thread:

Unicode assigns characters to ordinal numbers (in decimal form). (These numbers are called code points.)

à -> 224

UTF-8 is an encoding that 'translates' these ordinal numbers (in decimal form) to binary representations.

224 -> 11000011 10100000

Note that we're talking about the binary representation of 224, not its binary form, which is 0b11100000.

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I have checked the links in Gumbo's answer, and I wanted to paste some part of those things here to exist on Stack Overflow as well.

"...Some people are under the misconception that Unicode is simply a 16-bit code where each character takes 16 bits and therefore there are 65,536 possible characters. This is not, actually, correct. It is the single most common myth about Unicode, so if you thought that, don't feel bad.

In fact, Unicode has a different way of thinking about characters, and you have to understand the Unicode way of thinking of things or nothing will make sense.

Until now, we've assumed that a letter maps to some bits which you can store on disk or in memory:

A -> 0100 0001

In Unicode, a letter maps to something called a code point which is still just a theoretical concept. How that code point is represented in memory or on disk is a whole other story..."

"...Every platonic letter in every alphabet is assigned a magic number by the Unicode consortium which is written like this: U+0639. This magic number is called a code point. The U+ means "Unicode" and the numbers are hexadecimal. U+0639 is the Arabic letter Ain. The English letter A would be U+0041...."

"...OK, so say we have a string:

Hello

which, in Unicode, corresponds to these five code points:

U+0048 U+0065 U+006C U+006C U+006F.

Just a bunch of code points. Numbers, really. We haven't yet said anything about how to store this in memory or represent it in an email message..."

"...That's where encodings come in.

The earliest idea for Unicode encoding, which led to the myth about the two bytes, was, hey, let's just store those numbers in two bytes each. So Hello becomes

00 48 00 65 00 6C 00 6C 00 6F

Right? Not so fast! Couldn't it also be:

48 00 65 00 6C 00 6C 00 6F 00 ? ..."

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This article explains all the details http://kunststube.net/encoding/

WRITING TO BUFFER

if you write to a 4 byte buffer, symbol あ with UTF8 encoding, your binary will look like this:

00000000 11100011 10000001 10000010

if you write to a 4 byte buffer, symbol あ with UTF16 encoding, your binary will look like this:

00000000 00000000 00110000 01000010

As you can see, depending on what language you would use in your content this will effect your memory accordingly.

e.g. For this particular symbol: あ UTF16 encoding is more efficient since we have 2 spare bytes to use for the next symbol. But it doesn't mean that you must use UTF16 for Japan alphabet.

READING FROM BUFFER

Now if you want to read the above bytes, you have to know in what encoding it was written to and decode it back correctly.

e.g. If you decode this : 00000000 11100011 10000001 10000010 into UTF16 encoding, you will end up with 臣 not あ

Note: Encoding and Unicode are two different things. Unicode is the big (table) with each symbol mapped to a unique code point. e.g. あ symbol (letter) has a (code point): 30 42 (hex). Encoding on the other hand, is an algorithm that converts symbols to more appropriate way, when storing to hardware.

30 42 (hex) - > UTF8 encoding - > E3 81 82 (hex), which is above result in binary.

30 42 (hex) - > UTF16 encoding - > 30 42 (hex), which is above result in binary.

https://i.stack.imgur.com/6C0C6.png

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My explanation, after reading numerous posts and articles about this topic:

1 - The Unicode Character Table

"Unicode" is a giant table, that is 21bits wide, these 21bits provide room for 1,114,112 codepoints / values / fields / places to store characters in.

Out of those 1,114,112 codepoints, 1,111,998 are able to store Unicode characters, because there are 2048 codepoints reserved as surrogates, and 66 codepoints reserved as non-characters. So, there are 1,111,998 codepoints that can store a unique character, symbol, emoji and etc.

However, as of now, only 144,697 out of those 1,114,112 codepoints, have been used. These 144,697 codepoints contain characters that cover all of the languages, as well as symbols, emojis and etc.

Each character in the "Unicode" is assigned to a specific codepoint aka has a specific value / Unicode number. For Example the character "❤", has the following value aka Unicode number "U+2764". The value "U+2764" takes exactly one codepoint out of the 1,114,112 codepoints. The value "U+2764" looks like that in binary: "11100010 10011101 10100100", which is exactly 3 bytes or 24bits (without the two empty space characters, each of which taking 1 bit, but I have added them for visual purposes only, in order to make the 24bits more readable, so please ignore them).

Now, how is our computer supposed to know if those 3 byters "11100010 10011101 10100100" are to be read separate or together? If those 3 bytes are read separate and then converted to characters the result would be "Ô, Ø, ñ", which is quite the difference compared to our heart emoji "❤".

2 - Encoding Standarts (UTF-8, ISO-8859, Windows-1251 and etc)

In order to solve this problem people have invented the Encoding Standarts. The most popular one being UTF-8, since 2008. UTF-8 accounts for an average of 97.6% of all web pages, that is why we will UTF-8, for the example below.

2.1 - What is Encoding?

Encoding, simply said means to to convert something, from one thing to another. In our case we are converting data, more specifically bytes to the UTF-8 format, I would also like to rephrase that sentence as: "converting bytes to UTF-8 bytes", although it might not be technically correct.

2.2 Some information about the UTF-8 format, and why it's so important

UTF-8 uses a minimum of 1 bytes to store a character and a maximum of 4 bytes. Thanks to the UTF-8 format we can have characters which take more than 1 byte of information.

This is very important, because if it was not for the UTF-8 format, we would not be able to have such a vast diversity of alphabets, since the letters of some alphabets can't fit into 1 byte, We also wouldn't have emojis at all, since each one requires atleast 3 bytes. I am pretty sure you got the point by now, so let's continue forward.

2.3 Example of Encoding a Chinese character to UTF-8

Now, lets say we have the Chinese character "汉".

This character takes exactly 16 binary bits "01101100 01001001", thus as we discussed above, we can not read this character, unless we encode it to UTF-8, because the computer will have no way of knowing, if these 2 bytes are to be read seperately or together.

Converting this "汉" character's 2 bytes into, as I like to call it UTF-8 bytes, will result in the following:

(Normal Bytes) "01101100 01001001" -> (UTF-8 Encoded Bytes) "11100110 10110001 10001001"

Now, how did we end up with 3 bytes instead of 2? How is that supposed to be UTF-8 Encoding, turning 2 bytes into 3?

In order to explain how the UTF-8 encoding works, I am going to literally copy the reply of @MatthiasBraun, a big shoutout to him for his terrific explanation.

2.4 How does the UTF-8 encoding actually work?

What we have here is the template for Encoding bytes to UTF-8. This is how Encoding happens, pretty exciting if you ask me!

Now, take a good look at the table below and then we are going to go through it together.

        Binary format of bytes in sequence:

        1st Byte    2nd Byte    3rd Byte    4th Byte    Number of Free Bits   Maximum Expressible Unicode Value
        0xxxxxxx                                                7             007F hex (127)
        110xxxxx    10xxxxxx                                (5+6)=11          07FF hex (2047)
        1110xxxx    10xxxxxx    10xxxxxx                  (4+6+6)=16          FFFF hex (65535)
        11110xxx    10xxxxxx    10xxxxxx    10xxxxxx    (3+6+6+6)=21          10FFFF hex (1,114,111)

The "x" characters in the table above represent the number of "Free Bits", those bits are empty and we can write to them. The other bits are reserved for the UTF-8 format, they are used as headers / markers. Thanks to these headers, when the bytes are being read using the UTF-8 encoding, the computer knows, which bytes to read together and which seperately. The byte size of your character, after being encoded using the UTF-8 format, depends on how many bits you need to write. In our case the "汉" character is exactly 2 bytes or 16bits: "01101100 01001001" thus the size of our character after being encoded to UTF-8, will be 3 bytes or 24bits "11100110 10110001 10001001" because "3 UTF-8 bytes" have 16 Free Bits, which we can write to Solution, step by step below:

2.5 Solution:

        Header  Place holder    Fill in our Binary   Result         
        1110    xxxx            0110                 11100110
        10      xxxxxx          110001               10110001
        10      xxxxxx          001001               10001001 

2.6 Summary:

        A Chinese character:      汉
        its Unicode value:        U+6C49
        convert 6C49 to binary:   01101100 01001001
        encode 6C49 as UTF-8:     11100110 10110001 10001001

3 - The difference between UTF-8, UTF-16 and UTF-32

Original explanation of the difference between the UTF-8, UTF-16 and UTF-32 encodings: https://javarevisited.blogspot.com/2015/02/difference-between-utf-8-utf-16-and-utf.html

The main difference between UTF-8, UTF-16, and UTF-32 character encodings is how many bytes they require to represent a character in memory:

UTF-8 uses a minimum of 1 byte, but if the character is bigger, then it can use 2, 3 or 4 bytes. UTF-8 is also compatible with the ASCII table.

UTF-16 uses a minimum of 2 bytes. UTF-16 can not take 3 bytes, it can either take 2 or 4 bytes. UTF-16 is not compatible with the ASCII table.

UTF-32 always uses 4 bytes.

Remember: UTF-8 and UTF-16 are variable-length encodings, where UTF-8 can take 1 to 4 bytes, while UTF-16 will can take either 2 or 4 bytes. UTF-32 is a fixed-width encoding, it always takes 32 bits.

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They are the same thing, aren't they?

No, they aren't.

I think the first sentence of the Wikipedia page you referenced gives a nice, brief summary:

UTF-8 is a variable width character encoding capable of encoding all 1,112,064 valid code points in Unicode using one to four 8-bit bytes.

To elaborate:

Unicode is a standard, which defines a map from characters to numbers, the so-called code points, (like in the example below). For the full mapping, you can have a look here. ! -> U+0021 (21), " -> U+0022 (22), \# -> U+0023 (23)

UTF-8 is one of the ways to encode these code points in a form a computer can understand, aka bits. In other words, it's a way/algorithm to convert each of those code points to a sequence of bits or convert a sequence of bits to the equivalent code points. Note that there are a lot of alternative encodings for Unicode.

Joel gives a really nice explanation and an overview of the history here.

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UTF-8 is a method for encoding Unicode characters using 8-bit sequences.

Unicode is a standard for representing a great variety of characters from many languages.

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As a simple answer that gets straight to the point:

Unicode is a standard for representing characters from many human languages.

UTF-8 is a method for encoding Unicode characters.

* Yes: I'm overlooking the inner workings of UTF-8 on purpose.

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So you end up here usually from Google, and want to try different stuff. But how do you print and convert all these character sets?

Here I list a few useful one-liners.

In Powershell:

# Print character with the Unicode point (U+<hexcode>) using this: 
[char]0x2550

# With Python installed, you can print the unicode character from U+xxxx with:
python -c 'print(u"\u2585")'

If you have more Powershell trix or shortcuts, please comment.

In Bash, you'd appreciate the iconv, hexdump and xxd from the libiconv and util-linux packages (probably named differently on other *nix distros.)

# To print the 3-byte hex code for a Unicode character:
printf "\\\x%s" $(printf '═'|xxd -p -c1 -u)
#\xE2\x95\x90

# To print the Unicode character represented by hex string:
printf '\xE2\x96\x85'
#▅

# To convert from UTF-16LE to Unicode
echo -en "════"| iconv -f UTF-16LE -t UNICODEFFFE

# To convert a string into hex: 
echo -en '═�'| xxd -g 1
#00000000: e2 95 90 ef bf bd

# To convert a string into binary:
echo -en '═�\n'| xxd -b
#00000000: 11100010 10010101 10010000 11101111 10111111 10111101  ......
#00000006: 00001010

# To convert a binary string into hex:
printf  '%x\n' "$((2#111000111000000110000010))"
#e38182

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