{
    "name": "Password Entropy Calculator",
    "url": "https://calculators.geekmidst.com/calculators/password-entropy-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/password-entropy-calculator.md",
    "category": "IT, networking & security",
    "description": "Calculate the entropy in bits of a randomly generated password or Diceware-style passphrase from its length and the size of the character set or word list.",
    "summary": "Entropy measures how many equally likely choices a random generator could have made: length × log₂(pool size). It applies to passwords picked at random, not to ones people make up.",
    "also_called": [
        "Passphrase entropy calculator",
        "Password bits calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "mode",
            "label": "Type",
            "type": "segmented",
            "default": "chars",
            "options": {
                "chars": "Random characters",
                "words": "Random words"
            }
        },
        {
            "name": "length",
            "label": "Length",
            "type": "number",
            "default": "12",
            "unit": "characters",
            "shown_when": {
                "mode": "chars"
            }
        },
        {
            "name": "charset",
            "label": "Characters drawn from",
            "type": "select",
            "default": "alnum",
            "options": {
                "digits": "Digits only (10)",
                "lower": "Lower-case letters (26)",
                "lower_digits": "Lower case + digits (36)",
                "alnum": "Upper + lower + digits (62)",
                "ascii": "All printable ASCII (94)",
                "custom": "Custom pool size"
            },
            "shown_when": {
                "mode": "chars"
            }
        },
        {
            "name": "pool_size",
            "label": "Characters in the pool",
            "type": "number",
            "default": "70",
            "shown_when": {
                "charset": "custom"
            }
        },
        {
            "name": "words",
            "label": "Number of words",
            "type": "number",
            "default": "6",
            "shown_when": {
                "mode": "words"
            }
        },
        {
            "name": "wordlist",
            "label": "Words in the list",
            "type": "number",
            "default": "7776",
            "shown_when": {
                "mode": "words"
            }
        }
    ],
    "outputs": [
        {
            "key": "entropy_bits",
            "label": "Entropy",
            "format": "number"
        },
        {
            "key": "bits_per_symbol",
            "label": "Bits per character or word",
            "format": "number"
        },
        {
            "key": "combinations",
            "label": "Equally likely possibilities",
            "format": "text"
        },
        {
            "key": "equivalent_ascii_chars",
            "label": "Same as random printable-ASCII characters",
            "format": "number"
        }
    ],
    "formula": {
        "text": "Entropy (bits) = L × log₂ N;  Possibilities = N^L",
        "variables": {
            "L": "number of characters or words",
            "N": "characters in the pool or words in the list"
        }
    },
    "worked_example": {
        "inputs": {
            "mode": "chars",
            "length": "12",
            "charset": "alnum",
            "pool_size": "70",
            "words": "6",
            "wordlist": "7776"
        },
        "steps": [
            "Pool: 26 + 26 + 10 = 62 characters; log₂ 62 = 5.9542 bits each.",
            "12 × 5.9542 = 71.45 bits.",
            "62¹² = 3.23 × 10²¹ possible passwords."
        ],
        "result": "A random 12-character password from upper and lower case letters and digits has 71.45 bits of entropy."
    },
    "interpretation": "Each extra bit doubles the guesses needed. Compare the result with an attacker’s guess rate in the Password Brute-Force Time Calculator to see what it means in time.",
    "assumptions": [
        "Every character or word is chosen independently and uniformly at random, as a password manager or dice do."
    ],
    "limitations": [
        "Human-chosen passwords have far less entropy than their length suggests, because attackers guess common words and patterns first. This calculator does not rate a password you type."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why not type my password in to check it?",
            "answer": "Entropy belongs to the method that produced the password, not the string. “Password1!” uses four character types but is among the first guesses any cracker tries."
        },
        {
            "question": "Words or characters?",
            "answer": "Six Diceware words (77.5 bits) beat 12 random alphanumerics (71.5 bits) and are much easier to type and remember."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Password Brute-Force Time Calculator",
            "url": "https://calculators.geekmidst.com/calculators/password-brute-force-time-calculator"
        },
        {
            "name": "Password Generator",
            "url": "https://calculators.geekmidst.com/calculators/password-generator"
        },
        {
            "name": "PBKDF2 Runtime Calculator",
            "url": "https://calculators.geekmidst.com/calculators/pbkdf2-runtime-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}