Encoders & Decoders

Base64 Encoder / Decoder

Encode text or files to Base64 or decode Base64 back to text. Supports image preview, data URL output, and one-click direction swap — nothing sent to a server.

Encode & Decode
Text & File Input
Data URL Output
Image Preview
Browser-only

Text to Encode

Enter text or a file above and click Encode / Decode

Base64 Encoding: RFC 4648 Principles & Applications

Base64 is a binary-to-text encoding scheme standardized under RFC 4648. It translates arbitrary binary data (such as compiled executables, raw images, or cryptographic keys) into an ASCII string representation composed of 64 printable characters. This enables binary transmission across text-only protocols like HTTP headers, email (MIME), and JSON payloads without data corruption.

The Mathematics of Base64 Encoding

Base64 maps consecutive 24-bit chunks of binary data (3 bytes) into four 6-bit index values:

$$\frac{24 \text{ bits}}{6 \text{ bits/char}} = 4 \text{ encoded characters}$$

Because $2^6 = 64$, each 6-bit block maps directly to one character in the Base64 alphabet: A-Z (indices 0-25), a-z (indices 26-51), 0-9 (indices 52-61), + (index 62), and / (index 63).

Binary Representation	Hex Bytes	Encoded Base64 Output
`01001101 01100001 01101110`	`4D 61 6E` ("Man")	`TWFu`
`01000001` (1 byte)	`41` ("A")	`QQ==` (padded with two `=` signs)
`01000001 01000010` (2 bytes)	`41 42` ("AB")	`QUI=` (padded with one `=` sign)

Data Overhead & URL-Safe Base64

Base64 increases raw payload size by approximately 33% ($4 / 3 = 1.333$). Standard Base64 contains + and /, which carry special reserved meanings in URL query parameters. URL-Safe Base64 substitutes - for + and _ for /, frequently omitting trailing = padding characters.

Encoding and Decoding Base64 in Code

JavaScript

// Browser & Node.js
function utf8ToBase64(str) {
  return btoa(unescape(encodeURIComponent(str)));
}

function base64ToUtf8(b64) {
  return decodeURIComponent(escape(atob(b64)));
}

Python

import base64

raw_bytes = b"BestToolOnline Developer Suite"
encoded = base64.b64encode(raw_bytes).decode("ascii")
print("Base64:", encoded)

decoded = base64.b64decode(encoded).decode("utf-8")
print("Decoded:", decoded)

Frequently Asked Questions

Why does Base64 encoding increase data size by approximately 33%?: Base64 maps every 3 binary bytes (24 bits) into 4 printable ASCII characters (6 bits each). Because 4 characters represent 3 bytes of input, data size expands by a factor of 4/3 (~33.3%).
What is the difference between standard Base64 and URL-safe Base64?: Standard Base64 contains + and / characters which have reserved meanings in URL query strings. URL-safe Base64 replaces + with - and / with _, often omitting trailing padding = characters.
What is Base64?: Base64 is an encoding scheme that converts binary data into a text representation using 64 characters (A-Z, a-z, 0-9, +, /). It is widely used to embed binary data like images in JSON, HTML, or email where binary data cannot be directly embedded.
Is Base64 encryption?: No. Base64 is an encoding scheme, not encryption. It does not provide any security or confidentiality - anyone can decode a Base64 string instantly. Do not use Base64 to protect sensitive data.
When should I use Base64?: Common uses include: embedding images as data URLs in HTML/CSS, encoding binary data for JSON APIs, encoding email attachments (MIME), and storing binary data in text-only formats like XML.
Is my data safe?: Yes. All encoding and decoding happens entirely in your browser using JavaScript's built-in btoa() and atob() functions. Your text and files are never sent to any server.
Why is Base64 output longer than the input?: Base64 encodes every 3 bytes of input as 4 characters, adding approximately 33% overhead. This is the trade-off for binary-safe text representation.
Can I encode images and files?: Yes. Use the File mode to upload any file. The tool reads it as a data URL and extracts the Base64 portion. You can use the output as a data URI directly in HTML: <img src="data:image/png;base64,...">

Accuracy & Advisory Notice: Base64 Encoder / Decoder

This website and utility are provided for general informational, calculation, and educational purposes only. Always verify critical computation outputs prior to professional deployment or financial use. See our Terms of Service and Privacy Policy for full governance details.

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Base64 Encoding: RFC 4648 Principles & Applications

The Mathematics of Base64 Encoding

Base64 maps consecutive 24-bit chunks of binary data (3 bytes) into four 6-bit index values:

$$\frac{24 \text{ bits}}{6 \text{ bits/char}} = 4 \text{ encoded characters}$$

Because $2^6 = 64$, each 6-bit block maps directly to one character in the Base64 alphabet: A-Z (indices 0-25), a-z (indices 26-51), 0-9 (indices 52-61), + (index 62), and / (index 63).

Binary Representation

Hex Bytes

Encoded Base64 Output

01001101 01100001 01101110

4D 61 6E ("Man")

TWFu

01000001 (1 byte)

41 ("A")

QQ== (padded with two = signs)

01000001 01000010 (2 bytes)

41 42 ("AB")

QUI= (padded with one = sign)

Encoding and Decoding Base64 in Code

JavaScript

// Browser & Node.js function utf8ToBase64(str) { return btoa(unescape(encodeURIComponent(str))); } function base64ToUtf8(b64) { return decodeURIComponent(escape(atob(b64))); }

Python

import base64 raw_bytes = b"BestToolOnline Developer Suite" encoded = base64.b64encode(raw_bytes).decode("ascii") print("Base64:", encoded) decoded = base64.b64decode(encoded).decode("utf-8") print("Decoded:", decoded)

Frequently Asked Questions

Why does Base64 encoding increase data size by approximately 33%?

Base64 maps every 3 binary bytes (24 bits) into 4 printable ASCII characters (6 bits each). Because 4 characters represent 3 bytes of input, data size expands by a factor of 4/3 (~33.3%).

What is the difference between standard Base64 and URL-safe Base64?

Standard Base64 contains + and / characters which have reserved meanings in URL query strings. URL-safe Base64 replaces + with - and / with _, often omitting trailing padding = characters.

What is Base64?

Base64 is an encoding scheme that converts binary data into a text representation using 64 characters (A-Z, a-z, 0-9, +, /). It is widely used to embed binary data like images in JSON, HTML, or email where binary data cannot be directly embedded.

Is Base64 encryption?

No. Base64 is an encoding scheme, not encryption. It does not provide any security or confidentiality - anyone can decode a Base64 string instantly. Do not use Base64 to protect sensitive data.

When should I use Base64?

Common uses include: embedding images as data URLs in HTML/CSS, encoding binary data for JSON APIs, encoding email attachments (MIME), and storing binary data in text-only formats like XML.

Is my data safe?

Yes. All encoding and decoding happens entirely in your browser using JavaScript's built-in btoa() and atob() functions. Your text and files are never sent to any server.

Why is Base64 output longer than the input?

Base64 encodes every 3 bytes of input as 4 characters, adding approximately 33% overhead. This is the trade-off for binary-safe text representation.

Can I encode images and files?

Yes. Use the File mode to upload any file. The tool reads it as a data URL and extracts the Base64 portion. You can use the output as a data URI directly in HTML: <img src="data:image/png;base64,...">