Arbitrary File to Base64 String Encoder & Decoder
Convert PDFs, ZIP archives, images, and binary binaries to base64 strings and decode base64 back into downloadable original files. 100% computed inside your browser with zero data sent to any server.
Click, drag & drop, or paste (Ctrl+V) any arbitrary file here
Supports PDFs, ZIP archives, images (PNG, JPG, WebP), audio (MP3, WAV), executables, and raw binaries. 100% computed inside your browser RAM.
Complete Guide: File to Base64 String Encoding & Decoding
Base64 encoding translates arbitrary binary octets into a safe 64-character ASCII repertoire (A-Z, a-z, 0-9, +, /). It enables embedding PDFs, ZIP archives, fonts, and images directly inside text mediums such as JSON payloads, HTML Data URIs, XML files, and email MIME attachments.
100% In-Browser Privacy
Your private files and sensitive PDFs never touch any cloud server. Every single byte is converted locally using browser native Web APIs (FileReader, Web Crypto, and Uint8Array streams).
+33.3% Base64 Expansion
Base64 maps every 3 bytes (24 bits) into 4 characters (6 bits each). This results in an exact expansion ratio of 4/3 (~133.3% of the original binary size), plus minor padding characters (=).
Automatic File Recovery
When decoding raw base64, our engine automatically detects magic byte headers (%PDF, PK zip, PNG, JPEG, GIF, MP3, WASM) to reconstruct the correct MIME type and extension without manual guessing.
Common Binary Signatures (Magic Numbers) Reference Table
| Format | MIME Type | Magic Bytes (Hex) | ASCII Header |
|---|---|---|---|
| PDF Document | application/pdf | 25 50 44 46 | %PDF- |
| ZIP Archive | application/zip | 50 4B 03 04 | PK.. |
| PNG Image | image/png | 89 50 4E 47 0D 0A 1A 0A | .PNG.... |
| JPEG Image | image/jpeg | FF D8 FF | ... |
| WebAssembly | application/wasm | 00 61 73 6D | \0asm |
| GZip Archive | application/gzip | 1F 8B | .. |
| TAR Archive | application/x-tar | 75 73 74 61 72 (at offset 257) | ustar |
Frequently Asked Questions (FAQ)
How does decoding Base64 back into an original downloadable file work?
The decoder sanitizes the Base64 input, parses it through a high-performance chunked byte engine into an 8-bit byte array, analyzes the magic number signatures, and constructs a standard W3C `Blob`. You can then immediately trigger a browser download to save the exact binary file with 100% byte fidelity and identical SHA-256 checksums.
What is the Data URI scheme format?
A Data URI follows the RFC 2397 specification: `data:[mediatype][;base64],data`. For example: `data:application/pdf;base64,JVBERi0x...` or `data:image/png;base64,iVBORw...`. Our decoder automatically strips CSS url wrappers, HTML tags, and Data URI headers while preserving declared MIME types to configure output files.
Is there any limit on file sizes?
Because processing is executed client-side inside browser RAM, we recommend files under 50MB for optimal responsiveness. For large strings, our editor provides truncated viewports and direct .txt file downloads so your browser UI stays silky smooth.