Security

Password Entropy Calculator

Estimate password entropy from length and character set assumptions.

Last reviewed: April 30, 2026Free toolMethodology

Password Entropy Calculator

These fields start with sample inputs. Keep them or replace them, then run the tool to show a fresh result.

Number fields accept plain values and common formatted input such as 250000, 250,000, or 1,234.56.

Result

Calculating the sample result.

Why it matters

Entropy estimates help teams reason about password strength in a way that is more concrete than vague labels like weak or strong.

When to use

  • Reviewing password policy ideas
  • Comparing randomly generated secrets of different lengths
  • Explaining why character set size and length both matter

Inputs & Outputs

Inputs

  • Password length is the number of characters in the password.
  • Character set size is the number of possible symbols that could appear in each position.

Outputs

  • Entropy bits estimate the search space complexity.
  • Combinational space shows the total number of possible passwords under the stated assumptions.

Entropy method

Entropy is calculated as password length multiplied by the base-2 logarithm of the available character set size.

Entropy bits = length x log2(character set size)

Worked example

1

Policy comparison

A team wants to compare a 16-character password from a 62-character set with shorter alternatives.

Inputs

  • Length: 16
  • Character set size: 62

Steps

  • Entropy = 16 x log2(62)

Result

  • The estimate shows why a modest increase in length can materially improve entropy.

Edge cases & caveats

  • Entropy estimates assume random generation, not human-chosen patterns.
  • A long but predictable password can still be weak in practice.

Frequently Asked Questions

Does entropy guarantee real-world security?

No. It is a useful estimate for random passwords, but real-world strength also depends on storage, rate limits, and user behavior.

Why is length so powerful?

Because each extra character multiplies the total search space, especially when the character set is broad.

Keep going

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