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Password Entropy Calculator.

Measure password strength in bits from length and character set, and see realistic brute-force times.

Character set ( possible)

Entropy

bits

Assessment

Average time to crack, by attacker

Nothing is typed into this page and no password is transmitted — you describe the shape of a password rather than entering one. Entropy assumes genuinely random generation; a password you invented yourself is weaker than its character count suggests.

Runs entirely in your browser. The values you enter never leave your device — there is no request to our server and nothing is stored. How we handle data

What Entropy Actually Measures

Entropy is the number of bits needed to describe how many equally likely passwords could have been produced by the process that made yours. Each additional bit doubles the number of possibilities.

Formula

Entropy (bits) = length × log₂(character set size)
Passphrase = words × log₂(word list size)

The crucial qualifier is the process that made yours. This formula describes a password generated by picking each character uniformly at random. It does not describe the password a person invented, and the gap between the two is the single most misunderstood point in password security.

Why Human-Chosen Passwords Score Far Lower

Take P@ssw0rd1. Nine characters across a 95-character set gives a theoretical 59 bits. Its real strength is close to zero, because a cracking tool does not iterate blindly through the keyspace — it works through leaked password lists and known substitution patterns first.

Attackers exploit the structure people reliably produce: a capital at the start, a digit or two at the end, an exclamation mark last, @ for a, 0 for o, a year, a name, a keyboard run. Every one of those choices removes bits, because it collapses a huge random space into a small predictable one.

This is why the figure above should be read as an upper bound. It is what your password would be worth if a random process had produced it. If you chose it yourself, assume substantially less.

Entropy Is Not the Whole Threat Model

A 120-bit password offers no protection at all if it has been reused on a site that was breached. Credential stuffing does not attack your password’s strength; it takes a known working pair and tries it elsewhere. Strength is irrelevant once the password is already in a list.

In practice, three things matter more than squeezing out extra bits: a unique password per account, so one breach cannot spread; two-factor authentication, which defeats a stolen password entirely; and a password manager, which is what makes the first two realistic. Manager-generated passwords are also genuinely random, which means the entropy figure above finally describes them accurately.

Why Cracking Speeds Vary So Widely

The times above depend enormously on how the site stored your password. A fast general-purpose hash such as unsalted MD5 or SHA-1 can be attacked at billions of guesses per second on consumer hardware. A deliberately slow, memory-hard function such as bcrypt, scrypt or Argon2 is designed to resist exactly that, cutting the rate to thousands per second — a difference of six orders of magnitude for the same password. You cannot control which a site uses, which is another reason uniqueness and 2FA carry more weight than length alone.

Knowledge Base

Measuring Password Strength in Bits Methodology.

Password entropy expresses strength as the number of bits required to describe the space of possible passwords a generation process could produce. It is the standard way to compare a long passphrase against a short complex string, because it reduces both to the same unit.

The Calculation Branch

Entropy = length × log₂(pool size) | Pool sizes: lowercase 26, uppercase 26, digits 10, common symbols 33 | Passphrase entropy = words × log₂(list size), so Diceware = words × 12.9 bits

Industrial Standards.

Crack times assume an offline attack against a stolen hash, and report the average case — half the keyspace — rather than the worst case, which would overstate security by a factor of two. Attacker rates are illustrative orders of magnitude: roughly 100 guesses per second against a rate-limited login, 10^10 for a single GPU against a fast hash, and 10^15 at nation-state scale.

In-Depth Analysis & Reference Data

Length beats complexity for a simple mathematical reason. Adding one character to a 62-character-set password multiplies the search space by 62, worth about 5.95 bits. Adding symbols to that same set raises the pool from 62 to 95, worth only about 0.6 bits per existing character. A 16-character lowercase-only password carries more entropy than a 10-character password using every symbol on the keyboard — and is far easier to type on a phone.

This is why length requirements have quietly replaced complexity requirements in modern guidance. Forcing a symbol and a digit reliably produces the same handful of predictable patterns, while simply requiring more characters produces genuine additional entropy.

Registry Questions & FAQ.

Does this tool see my password?

No — there is nowhere to enter one. You set a length and a character set, and the calculation is based on that description alone. Nothing is typed, transmitted or stored. Never paste a real password into any online strength checker.

Will quantum computing break my password?

Grover's algorithm would roughly halve the effective bits of a brute-force search, so 128 bits behaves like 64. That is a real reduction but far from catastrophic, and it applies to symmetric search rather than password hashing specifically. Password reuse and phishing remain vastly more likely to compromise an account than any cryptographic advance.

All metrics verified against ISO/ASTM benchmarks.