Binary Calculations

Binary Calculations

To perform subnetting operations, you will need to be proficient at converting decimal and binary numbers. When working with IP addresses, work with each octet separately. The following table shows the decimal value for various binary values with a single 1 bit.

Binary Value	10000000	01000000	00100000	00010000	00001000	00000100	00000010	00000001
Decimal Value	128	64	32	16	8	4	2	1

To find the decimal value of a number with multiple 1 bits, simply add the decimal value of the bits together. For example, the decimal value of the binary number 10010101 is:

10000000 = 128
00010000 = 16
00000100 = 4
00000001 = 1
Total = 128 + 16 + 4 + 1 = 149

To calculate the number of valid subnets or the number of hosts per subnet, you will need to know how to find the exponential values of 2. Use the following chart to identify the exponent values and the final possible number (after subtracting 2 from each exponent).

# of bits	1	2	3	4	5	6	7	8	9	10	11	12
Exponent	21	22	23	24	25	26	27	28	29	210	211	212
Exponent value	2	4	8	16	32	64	128	256	512	1024	2048	4096
Total number (-2)	0	2	6	14	30	62	128	254	510	1022	2046	4094

Tip: Memorize the shaded values. To find smaller or larger values, divide or multiply the exponent value by 2.