Understanding Base64 Encoding: How It Works and When to Use It
The definitive reference for understanding base64 encoding.
By RiseTop Team · May 2026 · 12 min read
What Is Base64 Encoding?
Base64 is a binary-to-text encoding scheme that represents binary data using a set of 64 printable ASCII characters (A-Z, a-z, 0-9, +, /). It converts every 3 bytes of binary data into 4 characters, making it safe to include in text-based formats like JSON, HTML, and email.
Key Property
3 bytes → 4 characters (33% size increase)
How Base64 Works
The encoding process:
Take 3 bytes of input (24 bits)
Split into 4 groups of 6 bits each
Map each 6-bit value to a Base64 character
If input isn't a multiple of 3, add = padding
✏️ Example
Encoding "Man": M (77), a (97), n (110) → binary: 01001101 01100001 01101110 → split into 6-bit groups: 010011 010110 000101 101110 → Base64: TWFu
Common Use Cases
Use Case
Example
Is It a Good Idea?
Email attachments
MIME encoding
✅ Standard practice
Data URLs
data:image/png;base64,...
⚠️ Small images only
API payloads
Binary data in JSON
⚠️ Increases payload by 33%
JWT tokens
Header + payload
✅ Standard practice
Storing images in DB
Base64 blob column
❌ Use file storage instead
CSS embedded images
background: url(data:...)
⚠️ Small icons only
Performance Considerations
Base64 has significant performance costs:
33% larger: 1MB file becomes 1.33MB when Base64 encoded
CPU overhead: Encoding/decoding requires CPU time
No compression: Base64 text doesn't compress as well as binary
Memory usage: Both the original and encoded version may be in memory
⚠️ Don't use Base64 for large files. For images over 10KB, use URLs to serve files directly. Base64 is only appropriate for small, frequently-accessed assets like icons and thumbnails.
No! Base64 is encoding, not encryption. Anyone can decode Base64 — it provides zero security. Never use it to hide sensitive data. Use proper encryption (AES, RSA) for security.
Can Base64 encode Unicode? +
Base64 works on bytes, not characters. To encode Unicode text, first convert it to UTF-8 bytes, then Base64 encode those bytes. Decode in reverse: Base64 decode → UTF-8 decode → text.
Why does Base64 increase file size by 33%? +
Base64 uses 4 characters to represent 3 bytes. Each character takes 1 byte (in UTF-8), so 3 bytes become 4 bytes — a 33% increase.