Base64 Encode Text and Files

Q: How do I Base64 encode Unicode text in JavaScript?

btoa() only accepts characters up to U+00FF and throws an error for anything else. Convert the string to UTF-8 bytes first, for example btoa(String.fromCharCode(...new TextEncoder().encode(str))). In Node.js, use Buffer.from(str, 'utf8').toString('base64').

Q: How do I Base64 encode on the command line?

Run printf '%s' 'your text' | base64 on Linux or macOS. GNU base64 wraps output at 76 characters by default (add -w 0 for a single line), and openssl base64 wraps at 64 (add -A).

Turn text, raw bytes or any file into Base64. Pick the character set the receiver expects, keep or drop the = padding, and wrap lines at 76 or 64 characters for MIME and PEM.

Variant Padding Line wrap Text encoding

Input

Open file

Output

Live

Runs entirely in your browser. Nothing is uploaded.

How to use

Type or paste the text to encode, switch the input to hex to encode raw bytes, or click Open file to encode a file.
Leave Text encoding on UTF-8 unless the receiving system expects another character set.
Set the options: keep the Standard variant for most uses, turn padding off if the receiver does not want it, and wrap lines at 76 (MIME) or 64 (PEM) characters when needed.
Copy the Base64 output or download it as a file.

How Base64 encoding works

The encoder reads the input three bytes at a time. Those 24 bits are split into four groups of 6 bits, and each 6-bit value (0 to 63) selects one character: A-Z for 0 to 25, a-z for 26 to 51, 0-9 for 52 to 61, then + and /. Three bytes in, four characters out, which is why Base64 is about 33% larger than the original data.

Text     M        a        n
Bytes    77       97       110
Bits     01001101 01100001 01101110
6-bit    010011 010110 000101 101110
Index    19     22     5      46
Base64   T      W      F      u

Padding and output length

When the input length is not a multiple of three, the last group is incomplete. One leftover byte becomes two characters followed by ==; two leftover bytes become three characters and one =. Padded output is therefore always 4 × ceil(n / 3) characters long for n input bytes.

Padding carries no data. JSON Web Tokens, URL parameters and many APIs leave it out, so turn padding off when the receiving side expects unpadded output. For links and file names, choose the URL-safe variant or use the Base64URL page, which replace + and / with - and _.

Line wrapping for MIME and PEM

By default the output is one long line, which is what JSON, data URIs and HTTP headers need. Two formats expect line breaks:

MIME, 76 characters. Email attachments sent with Content-Transfer-Encoding: base64 must not have lines longer than 76 characters (RFC 2045). This option ends lines with CRLF, as MIME requires.
PEM, 64 characters. Certificates and keys between -----BEGIN and -----END lines use 64-character lines (RFC 7468). This option uses LF line endings.

Character sets and files

Base64 encodes bytes, not letters, so text is first converted to bytes with a character set. The letter é is two bytes in UTF-8 but a single byte in ISO-8859-1 or Windows-1252, so the same text produces different Base64. UTF-8 is correct for the web, JSON and nearly every modern API; pick GBK, Shift_JIS, Windows-1251 or another charset only to match a legacy system.

Files are encoded exactly as stored, with no charset conversion. For images with ready-made HTML and CSS snippets, see Image to Base64; for a data URI with the detected MIME type, use File to Base64.

Specification

Alphabet	`A-Z a-z 0-9 + /`
Output size	4 characters per 3 bytes (about 133%)
Padding	= to a multiple of 4 characters
Standard	RFC 4648 section 4
Case sensitive	Yes

Examples

Input (UTF-8)	Output
`Hello, World!`	`SGVsbG8sIFdvcmxkIQ==`
`Base64.is`	`QmFzZTY0Lmlz`
`你好`	`5L2g5aW9`

Frequently asked questions

Why does my Base64 output differ from another encoder?

Almost always because the input bytes differ. Typical causes are a trailing newline (the shell command echo adds one; use printf '%s' or echo -n), a different character set, Windows line endings in the text, or different padding, alphabet or line-wrap settings. The same bytes with the same options always give the same output.

How do I Base64 encode Unicode text in JavaScript?

btoa() only accepts characters up to U+00FF and throws an error for anything else. Convert the string to UTF-8 bytes first, for example btoa(String.fromCharCode(...new TextEncoder().encode(str))). In Node.js, use Buffer.from(str, 'utf8').toString('base64').

How do I Base64 encode on the command line?

Run printf '%s' 'your text' | base64 on Linux or macOS. GNU base64 wraps output at 76 characters by default (add -w 0 for a single line), and openssl base64 wraps at 64 (add -A).

Is Base64 encoding a form of encryption?

No. Base64 has no key and anyone can reverse it with a Base64 decoder. It exists to move binary data through channels that only accept text, not to hide information.

How much larger does Base64 make my data?

Every 3 bytes become 4 characters, rounded up to a full group, so the output is about 33% larger. MIME line wrapping adds two more bytes (CRLF) per 76 characters.