Base64 Encode: Text to Base64

Convert Base64 back to text →

How do you encode text to Base64?

Base64 encoding rewrites your text's bytes as printable characters. Base64 exists to carry data through channels that accept only US-ASCII text. It is an encoding, not encryption: any decoder reverses it.

1. Read your text as UTF-8 bytes. The converter does this for you; by hand, look each character up and write its byte value.
2. Take the bytes 3 at a time, which is 24 bits.
3. Cut each group into 4 numbers of 6 bits.
4. Write each number as the character at that index in the 64-character alphabet.
5. Pad a short final group with = until it is 4 characters wide. Hi becomes SGk=.

Text to Base64 Conversion Table

Base64 writes data with 64 characters - A to Z, a to z, 0 to 9, plus (+) and slash (/) - and reserves the equals sign (=) for padding. Each row is one six-bit value and the character that stands for it, so a group's number and its character are the same lookup read in either direction. RFC 4648 s5 swaps the last two rows; the + at index 62 becomes - and the / at index 63 becomes _.

Padding in the final group

A final group of three bytes takes no padding; two bytes give three characters and one equals sign; one byte gives two characters and two equals signs. RFC 4648 requires the pad characters unless the specification that refers to it says otherwise, so a Base64 string whose length is not a multiple of four is incomplete.

The same value in each encoding

These rows are shared with the other encoders, so a value written here is the value every page in the family writes.

Every value below is the one the specification fixes, so a result that disagrees with a row here is a result to check. ASCII defines 128 characters, codes 0–127, using 7 bits; in practice each code is stored in one 8-bit byte with a leading 0.

Worked Example: "Hi" to Base64

One group of bits at a time, with the regrouping drawn out. The same twenty-four cells are cut at eight above and at six below, which is the whole of why 3 bytes become 4 characters.

Start with the first group. Its bytes are 48 69, which is 16 bits written out in the top row. A byte is 8 bits and holds 256 values, 0–255; a nibble is 4 bits. Base64 reads three bytes (24 bits) at a time and writes them as four characters of six bits each, so the output runs four characters for every three bytes - about a third larger than the input.

The second row is the same run of bits cut every 6 instead of every eight. Each six-bit group is a number from 0 to 63, and that number is a row in the table above. Here they are 18, 6, 36, which name S, G, k. Nothing is lost in the regrouping: the same bits are read a different width, which is why the result reverses exactly.

UTF-8 encodes each character in 1 to 4 bytes. Characters 0–127 use one byte identical to ASCII, so ASCII text is valid UTF-8. That is why the byte count, not the character count, decides the length of the result — a character outside US-ASCII takes more than one byte and therefore more than one sixth of a group.

Check it in reverse

The value goes back the way it came. Four characters give their four indices, the indices give 24 bits, and the bits give 3 bytes again. Nothing is carried alongside the result: the alphabet says what each character is worth and the pad says how much of the last group was real. To verify the result by hand, decode the Base64 output back to text and compare it with what you started from.

Worked examples: text to Base64

Each example gives the value first, then the working. Click a value to load it in the converter.

Every example above reverses exactly - read the same four-character groups back as bytes.

What Changes the Base64 Output?

Which alphabet is in use?

This page writes the standard alphabet. The URL-safe alphabet of RFC 4648 section 5 keeps the first 62 characters and swaps plus for minus (-) and slash for underscore (_), so the result passes through a URL or a file name unchanged.

Are the line breaks part of the result?

No. RFC 4648 forbids adding line breaks to Base64 output. MIME is the specification that asks for them: RFC 2045 wraps at no more than 76 characters a line and tells decoders to ignore every character that is not in the alphabet.

What can the result be pasted into?

Anything that carries plain US-ASCII text. The alphabet was chosen so that every character in it survives a mail gateway, a JSON string and a form field without being rewritten on the way.

Is this the encoding you need at all?

The three schemes protect different things and are not interchangeable. these encodings are not interchangeable - which encoding belongs in which place sets out which does what.

Text to Base64 in Code

Both standard libraries carry this conversion, so the one-liner below is the whole job. Check the result against the table above before you trust it in a pipeline.

Python: base64.b64encode('Hi'.encode()).decode()

JavaScript: btoa(unescape(encodeURIComponent('Hi')))

Common Mistakes

• Treating the result as protection. Base64 exists to carry data through channels that accept only US-ASCII text. It is an encoding, not encryption: any decoder reverses it.
• Losing the pad. RFC 4648 requires the pad characters unless the specification that refers to it says otherwise, so a Base64 string whose length is not a multiple of four is incomplete.
• Pasting a string that carries the other alphabet: a minus sign or an underscore in the middle of a value means it was written for a URL, and this page will name the character it cannot read.

Frequently Asked Questions

Related Conversions

• if the value is going into a link rather than a text field, percent-encode a value for a query string instead.
• to encode a file rather than a string, encode a picture as a data URI.
• if the value is going into markup, escape text so it cannot break markup instead.
• if what you have is already escaped, read entities back as plain characters first.
• when the Base64 holds a picture, decode a data URI back to a picture.
• if the string arrived from a URL, read a percent-encoded string as plain text before you encode it.

The rest of the family sits on the rest of the text encoding converters.