Shannon Entropy Calculator
Measure Shannon entropy in bits per character for any text.
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What is a Shannon entropy calculator?
English prose measures roughly 4 bits of entropy per character; a string drawn evenly from all 95 printable ASCII characters approaches 6.6. This calculator applies Shannon’s formula to your input’s character frequencies and reports bits per character plus total information content. Low numbers expose repetitive or predictable strings, which is why entropy is a quick first check on passwords and generated tokens.
How to use the Shannon Entropy
- 1 Enter the string or passage you want to measure.
- 2 Read bits per character first; it is the comparable figure.
- 3 Check total bits to gauge overall guessing difficulty.
- 4 Test variants side by side to see which is less predictable.
What you can use it for
- Estimating the randomness of a password or token.
- Comparing the entropy of two candidate strings.
- Teaching information theory with live examples.
- Checking how repetitive a piece of data is.
Frequently asked questions
What does bits per character mean?
The average information each character carries given the string’s own frequencies. “aaaa” scores 0 bits; a string using many characters equally often scores near the maximum for its alphabet.
How is entropy calculated?
With Shannon’s formula: for each distinct character, take its probability times the base-2 log of that probability, sum the results and negate. Multiply by length for total bits.
Can I use it to judge password strength?
As a first filter, yes. But frequency-based entropy can’t see that “Password2024!” follows a guessable pattern. How the string was generated matters as much as the number.
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