Entropy Calculator
Password strength in bits
Fórmula: Entropía = L × log₂(N)
Donde L es la longitud y N es el tamaño del pool de caracteres posibles.
Entropy Calculator: The Math Behind Secure Passwords
Entropy measures unpredictability. In cryptography and passwords, it's expressed in bits: each bit doubles the possible combinations. A password with 60 bits of entropy has 2^60 combinations — hard to crack, but not impossible today.
Our calculator applies the standard formula log2(pool^length), where 'pool' is the number of possible characters (lowercase, uppercase, digits, symbols) and 'length' is the total number of characters. It shows you exact entropy, estimated brute-force crack time, and quality level (weak/moderate/strong/very strong).
For 2026: <60 bits is weak, 60-80 is moderate, 80-100 is strong, >100 is very strong (military grade). Use it to size passwords, encryption keys, tokens, or seed phrases.
How does it work?
- 1Type the password or key
Enter the string whose entropy you want to calculate.
- 2Or configure parameters
Alternatively, specify length and character types (lowercase, uppercase, digits, symbols) to estimate entropy without exposing the real password.
- 3Review the result
You'll get the bit-entropy, crack time at 10^9 attempts/sec, and quality level.
Frequently Asked Questions
For online passwords (with rate limiting): 60+ bits are OK. For offline hashes (leaked databases): minimum 80 bits recommended. For encryption keys: 128+ bits (AES-128) or 256+ (AES-256).
Because entropy grows exponentially with length but only linearly with pool size. A 20-char lowercase-only password (94 bits) is stronger than a 12-char password with everything (78 bits).
Yes. The formula assumes uniform randomness. If your password is 'password123' or 'iloveyou', its real entropy is close to zero because it appears in dictionaries. Never use words, names, or common dates.