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SESK: Stuff Everyone Should Know · sesk.info/tech-base64-size

Base64 encoding turns every 3 bytes of data into how many text characters?

4 characters, so Base64 makes data about a third bigger.

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  1. 3 characters
  2. 4 characters ✔
  3. 6 characters

Why: Base64 takes 24 bits (3 bytes) at a time and splits them into four 6-bit groups. Each 6-bit group becomes one of 64 printable characters. Four out for every three in means about 33% growth.

Huh, didn't know that: The equals sign at the end of Base64 text is padding, used when the data does not divide evenly into 3-byte groups.

The dad joke
Base64 walked into a bar and ordered 3 drinks. The bartender handed over 4.
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References

Answer: 4 characters. Base64 takes 24 bits (3 bytes) at a time and splits them into four 6-bit groups. Each 6-bit group becomes one of 64 printable characters. Four out for every three in means about 33% growth.

  1. RFC 4648: The Base16, Base32, and Base64 Data Encodings www.rfc-editor.org/rfc/rfc4648.txt
    The encoding process represents 24-bit groups of input bits as output strings of 4 encoded characters.
    Checked 2026-10-10.

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