Password Entropy Calculator
Measure password entropy in bits from its character pool.
Calculated locally in your browser — your input never leaves the page.
How to use
- 1 Enter a password or passphrase to measure.
- 2 Read the entropy in bits and the inferred pool size.
- 3 Check the weak/fair/strong/excellent rating.
- 4 Add length or character types to raise the entropy.
About Password Entropy Calculator
The Password Entropy Calculator measures how much randomness a password or passphrase carries, expressed in bits.
It uses the standard model — length multiplied by the base-2 logarithm of the character pool — where the pool size grows as you mix in lowercase letters, uppercase letters, digits and symbols.
The result is a single number that quantifies resistance to a brute-force search of that pool.
Entropy is the cleanest way to compare two passwords objectively.
A short password drawn from a large alphabet can be weaker than a long one drawn from a small alphabet, and the bit count makes that trade-off visible.
The tool shows the entropy, the pool size it inferred from the character classes you used, and a plain rating of weak, fair, strong or excellent so the number has context.
It runs locally in your browser, so the text you measure is never transmitted.
Bear in mind that entropy measures brute-force resistance against the implied keyspace, not whether the text is a dictionary word or a predictable phrase — a famous quote scores high on entropy yet is easy to guess.
Use this to size random passwords and to understand why each extra character or character class matters.
FAQ
What entropy counts as strong?
As a rough guide, under 40 bits is weak, 40–59 fair, 60–89 strong and 90+ excellent. Aim well above 60 bits for accounts that matter.
Does high entropy mean my password is safe?
It measures brute-force resistance only. A high-entropy-looking phrase that is a known quote or pattern can still be guessed quickly.