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SESK: Stuff Everyone Should Know · sesk.info/tech-utf8-byte-length

In UTF-8, how many bytes can one Unicode scalar value take?

1 to 4 bytes, depending on the scalar value.

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  1. Always 2 bytes
  2. 1 to 4 bytes ✔
  3. Always 1 byte

Why: UTF-8 is variable length. Common English letters take 1 byte, many other scalar values take 2 or 3, and values above U+FFFF take 4. One displayed symbol can combine several scalar values.

Huh, didn't know that: Older UTF-8 designs allowed sequences up to 6 bytes; RFC 3629 cut it to 4 to match Unicode's range.

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Why did the emoji need four bytes? It had a lot of feelings to express.
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References

Answer: 1 to 4 bytes. UTF-8 is variable length. Common English letters take 1 byte, many other scalar values take 2 or 3, and values above U+FFFF take 4. One displayed symbol can combine several scalar values.

  1. RFC 3629: UTF-8, a transformation format of ISO 10646 www.rfc-editor.org/rfc/rfc3629.txt
    characters from the U+0000..U+10FFFF range (the UTF-16 accessible range) are encoded using sequences of 1 to 4 octets
    Checked 2026-10-10.

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