Write down the hex number; for example, use 2D.
Convert each digit to a decimal counterpart. In the hexadecimal system, the numbers go from 0-9 for single digits. Ten through 15 are represented as the letters A through F. In the example, the digits are 2 and 13.
Convert each to their place value. The rightmost place is 16 to the power of 0 or 1. Multiply it by 13 in the example to get 13. The second-to-right digit is 16 raised to the power of 1 or 16. Multiply it by 2 to get 32.
Add the two numbers -- 32 + 13 = 25. Therefore, the hexadecimal number 2D equals 45 in decimal notation.