Sorry I just realized I should have said base 62. That’s all the letters and numbers, plus digits, too.

The hashing step gives you a binary sequence, so you’re actually converting from base 2, not from base 10. You treat the result of the hash as a giant binary integer and then repeatedly divide by 62, keeping track of the remainder. 0 = 0, 1 = 1, …, 9 = 9, 10 = a, 11 = b, …, 36 = z, 37 = A, 38 = B …, 61 = Z