How to know the number of characters in a password ?

[royce]

starkk, length is usually unknown - but you can usually make some good guesses (and start small).

Also, brute force should be your last option. You should be trying wordlists, combinator, hybrid (wordlists+masks), wordlists+rules, and masks before you move on to brute force. Study https://hashcat.net/wiki/#core_attack_modes for hints. There's a whole world of better techniques waiting for you.