How random are three words?
Each word is selected independently from the 7,776-entry EFF long word list. Three words have 7,776³ possible combinations—470,184,984,576 possibilities, or about 38.8 bits.
How the default reaches about 65 bits
Seven uniformly random digits contribute about 23.3 bits, and one selection from eight safe symbols contributes 3 more bits. Combined with three random words, the displayed estimate is about 65 bits.
Is a three-word passphrase strong enough?
It depends on the threat and the system protecting it. Three words alone are not appropriate for a high-value credential exposed to offline guessing. A rate-limited login may reduce guessing opportunities, but four to six independent words or a fully random manager-generated password is safer.
Do not create a sentence
A grammatical phrase, quotation, lyric, or familiar expression is not equivalent to three independent selections. Keep the generated words unchanged and do not replace them with related or personal words.
Choose the right word count
Use the two-word password generator only for tighter compatibility needs. Use the general passphrase generator for four or more words, or the Diceware generator for a physical-dice workflow.