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If this is for your Bitwarden master password, 4 words would be the absolute minimum (if you are really having trouble with longer passphrases). Using 5 words is sufficiently secure, and you can use 6 or more if you are a high-value target or if you tend to worry a lot about your vault security.
The strength of a passphrase is roughly equivalent to the strength of a random character string in which the number of characters is double the number of words in the passphrase (e.g., a 12-character random password and a 6-word random passphrase are roughly equivalent in strength).