File to Base64 Converter (with data URI support, both directions)

Convert any file (image, PDF, and more) to a Base64 string or data URI, or decode a Base64 string / data URI back into a downloadable file. Everything runs in your browser — files are never sent to a server.

Tips

  • The File → Base64 mode accepts any file type — images, PDFs, audio, and more — and lets you copy both the data URI form and the plain Base64 string.
  • In Base64 → File mode, paste a full data URI starting with data: and the MIME type is detected automatically. For a plain Base64 string, select the MIME type manually.
  • Every conversion runs entirely in your browser's JavaScript — the file content or Base64 string is never sent to a server, which makes this safe for sensitive files.
  • To embed a small icon directly in CSS or HTML, paste the data URI output straight into background-image: url(...) or an <img> tag's src.
  • Base64 encoding makes the output about 33% larger than the original file, so converting very large files (tens of megabytes or more) can make your browser feel sluggish.

FAQ

Base64 is an encoding scheme that represents binary data (images, audio, executables, or any other format) using only 64 printable ASCII characters: A–Z, a–z, 0–9, +, and /. It is not encryption — it is simply a way to represent arbitrary bytes as safe, printable text.

A data URI embeds a file's content directly inside a URL as a Base64-encoded string, like data:image/png;base64,iVBOR.... Because it also carries the MIME type, you can drop it straight into an <img> tag's src attribute or a CSS background-image to display the image.

No. This tool's conversion (encoding and decoding via FileReader and Blob) runs entirely as JavaScript inside your browser. Neither the file content nor the resulting Base64 string is ever sent to a server.

Yes. If the pasted text is not a full data URI starting with data:, a MIME type dropdown appears — pick the original file format (image, PDF, text, and so on) manually before downloading.

Base64 repacks 8-bit binary data into 6-bit characters, so the encoded output is roughly 4/3 the size of the original — about a 33% increase. This overhead is an unavoidable property of how Base64 encoding works.
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Side Note — Why Base64 Makes Files 33% Larger

Base64 encoding exists because many transport channels — email, JSON, URLs — can only safely carry printable ASCII text. Sending arbitrary binary data (like an image or an executable) as-is risks corruption from stray control characters, so Base64 was devised to represent any binary payload using just 64 printable characters: A–Z, a–z, 0–9, +, and /.

Base64 slices 3 bytes (24 bits) of binary data into four 6-bit chunks and maps each chunk to one Base64 character. Repacking 8-bit binary into 6-bit characters means the encoded output ends up roughly 4/3 the size of the original — about 33% larger. That size increase is the price paid for text-safe transport.

This same trick is put to good use in data URIs, which embed small images directly in HTML or CSS as data:image/png;base64,.... Doing so avoids an extra HTTP request for tiny assets like icons, which can speed up page loads. But the roughly 33% size overhead and the loss of browser caching make it a poor fit for large image files.

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