Password Strength Tester (Entropy Bits)
Estimate password entropy in bits and the time an offline brute-force attacker would need at common cracking rates. Pure client-side โ your password is never sent anywhere.
Result
- Length9 characters
- Character pool95 candidate chars (lower + upper + digit + symbol)
- Theoretical search space2^59.1 โ 6.30e+17
- Mean crack time364.7 days
- Worst-case (full space)2.0 years
Step-by-step
- Detect character classes present โ pool size = 95.
- Entropy bits = length ร logโ(pool) = 9 ร 6.570 = 59.1 bits.
- Mean crack time = (search-space / 2) / attacker-rate.
How to use this calculator
- Type or paste the password into the input.
- Choose the attacker rate โ 10 G/s is the realistic modern baseline; pick higher for nation-state threat models.
- Read the entropy bits and the mean / worst-case crack-time. Flags below the result indicate why the number may be over-stated.
- Aim for โฅ 80 bits for accounts that matter; โฅ 128 for master passwords or encryption keys.
About this calculator
A passwordโs strength is best expressed as its entropy in bits โ logโ of the number of equally-likely passwords an attacker has to try. For a random 12-character string mixing upper, lower, digit, and symbol, that is about 78 bits โ strong enough to resist a single GPU rig for centuries on a non-cached hash. This tester computes the theoretical entropy from password length and the character classes it contains, then converts to mean crack-time at four common attacker speeds: rate-limited online, slow bcrypt offline, modern GPU, and state-actor cluster. It also flags weaknesses that ruin the entropy estimate: dictionary words, short length, and use of only one character class.
How it works โ the formula
entropy_bits = length ยท logโ(pool_size)
mean_crack_time = (2^entropy_bits / 2) / attacker_rateFor a uniformly random password from a pool of N characters, the number of equally-likely possibilities is N^length, so logโ gives the entropy in bits. Mean-case search costs half that. Real-world passwords are far less random; entropy bits are an upper bound on resistance to brute force, not on resistance to dictionary attacks.
Worked examples
- Inputs:
- pwd=password
- Output:
- ~37.6 bits but dictionary-flagged โ minutes
- Inputs:
- pwd=Tr0u4!H#9Vk2
- Output:
- ~78 bits โ ~years on a GPU rig
- Inputs:
- pwd=correct horse battery staple
- Output:
- ~92 bits โ centuries on a GPU rig (but only ~52 bits if attacker uses a word-list)
Limitations
- Entropy โ real security: dictionary + rule-based crackers find "high-entropy looking" passwords in seconds when they follow common patterns.
- No breach-list check โ use haveibeenpwned.com/Passwords for that.
- Attacker-rate selection is a coarse model โ real cracking speed depends on the specific hash function and hardware.
Educational estimate only โ for compliance use a tool that also checks against breach databases and known dictionaries.