Count bytes before characters
| Key size | Bytes | Hex digits | Base64 length |
|---|---|---|---|
| 128 bits | 16 | 32 | 24 |
| 192 bits | 24 | 48 | 32 |
| 256 bits | 32 | 64 | 44 |
The Base64 lengths include standard padding where needed. Encoding changes representation, not entropy. A 64-character Hex key represents 32 bytes; a 64-character UTF-8 string generally represents different bytes.
Choose the key required by the protocol
A receiving system must know the same key and algorithm. Truncating AES-256 to fit AES-128 does not preserve compatibility. Increasing the size on one side alone does not upgrade a stored ciphertext. The mode, nonce, authentication and key-management process remain necessary regardless of key length.
All AES variants use 128-bit blocks. The site generates all three key sizes with crypto.getRandomValues. Raw AES-192 uses a named compatibility backend; AES-128/256 use Web Crypto. Target browsers still need real testing, especially for the clipboard, Workers and downloads.
A UTF-8 example that catches length errors
Eight Chinese characters can occupy 24 UTF-8 bytes, rather than eight bytes. That can form a 192-bit byte sequence, but a memorable phrase is not automatically a strong random key. The tool validates decoded bytes rather than silently truncating, repeating or zero-padding the input.
Use a generated random key when a protocol expects raw bytes. Use password mode when a human supplies a password: PBKDF2 derives a key with a salt and a declared work factor. Copying a password into the raw-key box does not apply that derivation.
Keep the key and the recovery parameters
A raw key alone is not a complete recovery record. Save mode, nonce or IV, tag layout, AAD, encoding and padding/counter rules with ciphertext, while keeping the key separately. If you rotate a key, retain the old key for data that still needs it; this website does not manage key inventories or recover discarded values.
Related tools and reading
- Encrypt text
- Decrypt text
- Encrypt a file
- Generate a key
- What Is AES Encryption? Keys, Blocks and Recovery
- AES-GCM vs CBC vs CTR: Authentication and Parameters
- AES-128 vs AES-192 vs AES-256: Bytes and Encodings
Technical references
Updated October 16, 2026