How strong is a good password?

Password strength is measured as entropy, in bits: the higher, the longer it takes to guess. A 20-character password using upper and lower case, digits, and symbols has about 128 bits, far beyond what is considered safe. A passphrase is easier to remember; with the word list used here, 8 random words plus a number give about 67 bits, and each extra word adds about 7.3 bits. Everything is generated with a cryptographic random generator on your device; nothing is sent or stored.