Base64 Encoder and Decoder

Base64 is a binary-to-text encoding scheme that represents arbitrary byte data as a string of 64 printable ASCII characters. It is used wherever binary content needs to travel through a text-only channel: email attachments are Base64-encoded inside MIME messages, images are embedded in HTML and CSS files as Base64 data URIs, binary file contents are stored in JSON and XML documents, and HTTP Basic Authentication sends credentials as a Base64 string in the request header. The algorithm groups input bytes in sets of three, converts each group of 24 bits into four 6-bit values, and maps each 6-bit value to a character from the set A-Z, a-z, 0-9, + and /. If the input length is not divisible by three, one or two padding characters (=) are appended. This tool lets you encode any plain text to Base64, or paste a Base64 string to decode it back to plain text. Everything runs in your browser using JavaScript's built-in btoa() and atob() functions; nothing you enter is sent to a server. The encoder handles standard ASCII text; the decoder works on any valid Base64 string. Enter your text below to encode it, or switch to the decode tab to convert Base64 back to plain text.

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Mode

Input text

SGVsbG8gV29ybGQ=

Base64 encoded output

Input length11 chars

Output length16 chars

Size ratio1.45x

Base64 encoded text is approximately 33% larger than the original. Nothing is uploaded; all processing runs in your browser.

How it works

Encoding uses the browser's built-in btoa() function, which converts a string of Latin-1 characters to Base64. Decoding uses atob(), which reverses the process. If the input contains characters outside the Latin-1 range (such as accented or Unicode characters), the encoder first converts the text to a UTF-8 percent-encoded string and then encodes that. Invalid Base64 input in decode mode shows an error message. The size ratio is output length divided by input length, showing the overhead Base64 introduces.

Worked example

Input "Hello World" (11 characters). H encodes to 72 in ASCII, e to 101, and so on. The 11 bytes are grouped in sets of 3, converted to Base64 characters, and padded to a multiple of 4. The result is "SGVsbG8gV29ybGQ=" (16 characters), a size ratio of about 1.45x. Decoding "SGVsbG8gV29ybGQ=" returns "Hello World". These match the defaults pre-filled above.

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Frequently asked questions

What is Base64 used for?

Base64 is used to safely transmit binary data over channels that only handle plain text, such as email (MIME attachments), embedding images directly in HTML or CSS as data URIs, storing binary data in JSON, and encoding credentials in HTTP Basic Authentication headers. It converts arbitrary bytes to a set of 64 printable ASCII characters.

Does Base64 encrypt data?

No. Base64 is an encoding scheme, not encryption. Anyone who receives Base64-encoded text can decode it trivially. If you need to protect the data, you must encrypt it first and then optionally encode the ciphertext in Base64 for transport. Never treat Base64 as a security measure.

Why does Base64 output end with = or ==?

Base64 works on groups of 3 input bytes (24 bits) and converts them to 4 Base64 characters. If the input is not a multiple of 3 bytes, padding characters (=) are added at the end to make the output a multiple of 4 characters. One = means one byte of padding was needed; two == means two bytes.