When working with IT it is important to be familiar with the binary numbers, Hex numbers and Octal.

Decimal (base 10)
Numbers are made up using ten digits 0,1,2,3,4,5,6,7,8,9

The place values are shown below

10⁰=1
10¹=10
10²=10 * 10 =100
10³=10* 10 * 10 =1000
10⁴=10 * 10 * 10 * 10 =10000
10⁵=10 * 10 * 10 * 10 * 10 =100000

BINARY (base 2)

Numbers are made up using only two digits 0,1

The place values are shown below

2⁰=1
2¹=2
2²=2 * 2 =4
2³=2 * 2 * 2 =8
2⁴=2 * 2 * 2 * 2 = 16
2⁵=2 * 2 * 2 * 2 * 2 = 32
2⁶=2 * 2 * 2 * 2 * 2 * 2 = 64
2⁷=2 * 2 * 2 * 2 * 2 * 2 * 2 = 128

The following pattern for solving binary numbers to decimal numbers and decimal numbers to binary numbers should be used. Always remember to calculate from right to left instead of left to right. Also notice that each place doubles in value from right to left.

The above should be memorized. Later this will be important to remember when figuring out the number of subnets and hosts per subnets. Therefore, this skill must be practiced and reinforced as often as possible. Here are a few sample problems.

Example 1 (binary to decimal)

11001011 = 128 + 64 + 8 + 2 + 1 = 203

By writing out the chart and placing the 1's and 0's under the proper place in the chart, all that is left is to add up the place values that have 1's under them and the total will be the decimal number value.

01011110 = 64 + 16 + 8 + 4 + 2 = 94

27	26	25	24	23	22	21	20
128	64	32	16	8	4	2	1
0	1	0	1	1	1	1	0

To convert decimal numbers to binary numbers, place 1's in the place values until all the place values with 1's add up to the total. If any numbered place adds a value that is larger than the decimal number, 0's should be placed in those place values.

138 = 10001010 or

Another method for converting decimal numbers to binary numbers is the remainder method. Divide the decimal number by 2 and place write down a 1 if there is a remainder or a 0 if there is no remainder. Then divide the answer by 2 and write down a 1 if there is a remainder or a 0 if there is no remainder. The division process continues until there are 8 bits or place values of 1's or 0's. Be sure to write the 1's and 0's down in reverse order from right to left.

The work can be checked by placing the 1's and 0's back into the chart and adding up the place values that have 1's.

Hexadecimal (base 16)

16

16

16

16

From Greek, hexadecimal is a word meaning "sixteen."

Hexa=6 (hexagonal, hexagram, etc.)
Decimal=10
Hexadecimal=16

In the hexadecimal system, 6 letters are added to the standard 0-9 Arabic Numerals, to give you a numbering system with base 16, instead of base ten.

Numbers are made up using sixteen digits 0,1,2,3,4,5,6,7,8,9, A, B, C, D, E, F

The place values are shown below

16⁰=1
16¹=16
16²=16 * 16 = 256
16³=16 * 16 * 16 = 4069

Counting in Hexadecimal:

Count from 0 to 9, then count A, B, C, D, E, F.

Then you reach 10 (hexadecimal 10, which corresponds to decimal 16).

Count again: 11, 12, 13, 14, 15, 16, 17, 18 , 19, then use 1 and a letter: 1A, 1B, 1C, 1D, 1E, 1F.

Then you reach 20 (hexadecimal 20, which corresponds to decimal 32).

This continues forever. For instance,

Example 1 (Hexadecimal to Decimal)

B0 in hexadecimal = 176 in decimal:
(B[hex] * 16[decimal]) + (0 * 1).
Since B is 11 in decimal, this equation becomes
(11 * 16) + (0 * 1) = 11 * 16 = 176.

Example 2 (Hexadecimal to Decimal)

D4 in hexadecimal = 212 in decimal:
(D[hex] * 16[decimal]) + (4 * 1).
Since D is 13 in decimal, this equation becomes
(13 * 16) + (4 * 1) = 208 + 4= 212.

Here are a few more examples

Example 6 (decimal to hex)

218 in decimal = DA in hexadecimal

Example 7 (decimal to hex)

178 in decimal = B2 in hexadecimal:
178 = (11 * 16) + (2 * 1) =
(B * 16[hex.]) + (2 * 1) =
B2.

Here are a few more examples

Here are some more numbers in hexadecimal and decimal.
Try converting one form to the other, and back again, until you are comfortable with the process.

Hex.	Dec.	.	Hex.	Dec.	.	Hex.	Dec.
0	0		10	16		C8	200
1	1		11	17		F0	240
2	2		19	25		FF	255
9	9		1A	26		100	256
A	10		1B	27		3E8	1,000
B	11		1F	31		1000	4,096
C	12		20	32		10000	65,536
D	13		32	50		100000	1,048,576
E	14		64	100		FFFFFF	16,777,215
F	15		A0	160		1000000	16,777,216

There are two advantages of a hexadecimal system for computers:

1. You can store more information in the same space. In a hex code with two digits you can express the numbers 0 through 255. In a decimal code with two digits you can count from 0 to 99.

2. Hexadecimal (base 16) converts easily to binary (base 2), which is used by computers. A two digit hexadecimal number can range from 0 to 255, which can be expressed in eight digits of binary code (one byte).

Octal (base 8)

Octa=6 (Octagonal, Octagram, Octave, etc.)

INumbers are made up using eight digits 0,1,2,3,4,5,6,7

The place values are shown below

8⁰=1
8¹=8
8²=8 * 8 = 64
8³=8 * 8 * 8 = 512
8⁴=8 * 8 * 8 * 8 =4096
8 ⁵=8 * 8 * 8 * 8 =32768

Counting in Hexadecimal:

Example 1 (Octal to Decimal)

1025 in octal = 533 in decimal
(1 * 512) + (0*64) + (2 * 8) + (5 * 1)

Example 2 (Octal to Decimal)

25170 in octal = 10872 in decimal
(2 * 4096) + (5 * 512) + (1*64) + (7 * 8) + (0 * 1)

Now the Easy Stuff!!

Binary to Octal

If we compare the place value of octal to binary you should see a pattern

Every group of three binary matches one octal.

Example 1
The binary number 101011 = 53 octal

Example 2
Binary 10010111 = 227 octal

Example 3
Binary 101011100 = 534 octal

Binary to Hexadecimal

If we compare the place value of octal to binary you should see a pattern

Every group of four binary matches one hex.

Example 1
The binary number 101001 = 29 hex

Example 2
Binary 10010111 = 97 hex

Example 3
Binary 01011010 = 5A hex

Example 3
Binary 10111110 = BE hex