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Password Entropy Calculator

log₂(charset^length). Free online Password Entropy Calculator. Calculate password entropy online — fast, accurate, mobile-friendly, no signup needed.

Entropy (bits)
74.0391

Derivation

  1. ├── 01Givenlen = 12, charset = 72
  2. ├── 02Formulat × log₂(a)
  3. └── 03Compute Entropy (bits)74.0391
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§01What is

Understanding the Password Entropy Calculator

The Password Entropy Calculator computes Entropy (bits) from 2 inputs: length, charset size. log₂(charset^length).

Quick calculators for the math that shouldn’t need a notepad — instant, accurate, private to your browser. The Password Entropy Calculator sits in that toolkit — it log₂(charset^length). Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

t × log₂(a)

Where

len
Length
charset
Charset size
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Length = 12, Charset size = 72.

  1. 01Start by noting the input — Length: 12.
  2. 02Start by noting the input — Charset size: 72.
  3. 03Substitute these values into the formula: t × log₂(a)
  4. 04Compute Entropy (bits): the calculator returns 74.0391.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Password Entropy Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Length halved

len = 6 (from 12)

Keep every other input at its default and halve the length. See how entropy (bits) responds.

  1. 01New Length: 6
  2. 02Baseline Entropy (bits): 74.0391
  3. 03New Entropy (bits): 37.0196
  4. 04Entropy (bits) decreases by 50% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Length doubled

len = 24 (from 12)

Keep every other input at its default and double the length. See how entropy (bits) responds.

  1. 01New Length: 24
  2. 02Baseline Entropy (bits): 74.0391
  3. 03New Entropy (bits): 148.078
  4. 04Entropy (bits) increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Charset size halved

charset = 36 (from 72)

Keep every other input at its default and halve the charset size. See how entropy (bits) responds.

  1. 01New Charset size: 36
  2. 02Baseline Entropy (bits): 74.0391
  3. 03New Entropy (bits): 62.0391
  4. 04Entropy (bits) decreases by 16.2% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Charset size doubled

charset = 144 (from 72)

Keep every other input at its default and double the charset size. See how entropy (bits) responds.

  1. 01New Charset size: 144
  2. 02Baseline Entropy (bits): 74.0391
  3. 03New Entropy (bits): 86.0391
  4. 04Entropy (bits) increases by 16.2% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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