To convert DSCP AF values to decimal, multiply the first digit by 8, and the second digit by 2, and add the two values:

AF21 – (2*8) + (1*2) = 18

AF31 – (3*8) + (1*2) = 26

The process can be reversed by deviding the decimal value by 8, and the remainder by 2:

30 – 30/8 = 3, remainder of 6, 6/2 = 3 = AF33

CS codes can just be converted by multiplying by 8, CS3 = 24