To convert octal 123 to decimal: 3 * 8^0 = 3 * 1 = 3 2 * 8^1 = 2 * 8 = 16 1 * 8^2 = 1 * 64 = 64 Adding these results: 3 + 16 + 64 = 83. So, octal 123 is decimal 83.