In the hexadecimal system we have 16 numbers, ranging from 0 to 15, or from 0 to F: It starts with the "regular" 0, 1, 2, 3, 4, 5, 6, 7, 9. When we come to 10, we start displaying the numbers as letters: A, B, C, D, E, F.

A=10, B=11, C=12, D=13, E=14, F=15.

This works quite similar to converting from binary to decimal. We write down the a table, fill in the hexadecimal number and add up.