base 18 is a positional numeral system with eighteen as its base. It uses 18 different digits for representing numbers. The digits for base 18 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, and h.

base 16 is a positional numeral system with sixteen as its base. It uses 16 different digits for representing numbers. The digits for base 16 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, and f.