Different Worlds | An Introduction to HTML | Appendix C: Converting Numbers

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Appendix C: Hexadecimal Numbers

Conversion Chart

Each table cell contains a decimal value followed by the corresponding hexadecimal value. The numbers followed by "safe" are those which, in combination, produce the 216 "browser safe colours" (see Appendix B for a chart showing these colours).									0 00 (safe)
1 01	2 02	3 03	4 04	5 05	6 06	7 07	8 08	9 09	10 0A
11 0B	12 0C	13 0D	14 0E	15 0F	16 10	17 11	18 12	19 13	20 14
21 15	22 16	23 17	24 18	25 19	26 1A	27 1B	28 1C	29 1D	30 1E
31 1F	32 20	33 21	34 22	35 23	36 24	37 25	38 26	39 27	40 28
41 29	42 2A	43 2B	44 2C	45 2D	46 2E	47 2F	48 30	49 31	50 32
51 33 (safe)	52 34	53 35	54 36	55 37	56 38	57 39	58 3A	59 3B	60 3C
61 3D	62 3E	63 3F	64 40	65 41	66 42	67 43	68 44	69 45	70 46
71 47	72 48	73 49	74 4A	75 4B	76 4C	77 4D	78 4E	79 4F	80 50
81 51	82 52	83 53	84 54	85 55	86 56	87 57	88 58	89 59	90 5A
91 5B	92 5C	93 5D	94 5E	95 5F	96 60	97 61	98 62	99 63	100 64
101 65	102 66 (safe)	103 67	104 68	105 69	106 6A	107 6B	108 6C	109 6D	110 6E
111 6F	112 70	113 71	114 72	115 73	116 74	117 75	118 76	119 77	120 78
121 79	122 7A	123 7B	124 7C	125 7D	126 7E	127 7F	128 80	129 81	130 82
131 83	132 84	133 85	134 86	135 87	136 88	137 89	138 8A	139 8B	140 8C
141 8D	142 8E	143 8F	144 90	145 91	146 92	147 93	148 94	149 95	150 96
151 97	152 98	153 99 (safe)	154 9A	155 9B	156 9C	157 9D	158 9E	159 9F	160 A0
161 A1	162 A2	163 A3	164 A4	165 A5	166 A6	167 A7	168 A8	169 A9	170 AA
171 AB	172 AC	173 AD	174 AE	175 AF	176 B0	177 B1	178 B2	179 B3	180 B4
181 B5	182 B6	183 B7	184 B8	185 B9	186 BA	187 BB	188 BC	189 BD	190 BE
191 BF	192 C0	193 C1	194 C2	195 C3	196 C4	197 C5	198 C6	199 C7	200 C8
201 C9	202 CA	203 CB	204 CC (safe)	205 CD	206 CE	207 CF	208 D0	209 D1	210 D2
211 D3	212 D4	213 D5	214 D6	215 D7	216 D8	217 D9	218 DA	219 DB	220 DC
221 DD	222 DE	223 DF	224 E0	225 E1	226 E2	227 E3	228 E4	229 E5	230 E6
231 E7	232 E8	233 E9	234 EA	235 EB	236 EC	237 ED	238 EE	239 EF	240 F0
241 F1	242 F2	243 F3	244 F4	245 F5	246 F6	247 F7	248 F8	249 F9	250 FA
251 FB	252 FC	253 FD	254 FE	255 FF (safe)

What is "hexadecimal"?

The number system we use is based on units of 10. Single digit numbers go from 1 to 9, then 10 = 1 unit of 10 plus 0 single units.

The hexadecimal number system works in exactly the same way, except that it is based on units of 16. That means that 10_{(base 16)} = 1 unit of 16 plus 0 single units. That also means that we need some additional figures, since single digit numbers in hexadecimal run from 1 to 15. Rather than inventing new figures, the first 6 letters are used. So in hexadecimal, we have:

1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10
11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E, 1F, 20
21, 22, 23, etc to 9F, then A0
A1, A2, A3, etc, and so on up to FF, 100
101, 102, etc

Converting from decimal to hexadecimal

To convert from decimal to hexadecimal, all you have to do is divide by 16. However, you need to go back in time to when you were at school, and hadn't yet learned about fractions or decimals. So, for example, if you divide 24 by 16, you get "1 remainder 8". So 24 (which is 2 lots of 10 plus 4 single units) = 18_{(base 16)} (ie 1 lot of 16 plus 8 single units).

Let's look at a colour. The navy blue colour we used has a red value of 0. That's still 0 in hexadecimal, so the first two digits of the RGB value are "00". The green value is also 0, so now we have "0000". The blue value is 128. Divide that by 16. We get "8 remainder 0". So now we have "000080".

Another example: The yellow colour we used for the text has a red and a green value of 255. Divide that by 16. We get "15 remainder 15". When writing hexadecimal numbers, remenber that 11=A, 12=B, 13=C, 14=D and 15=F. So "15 remainder 15" = FF. Since the blue value is 0, the full hexadecimal RGB value for this particular shade of yellow is "FFFF00".

Converting from hexadecimal to decimal

If for some reason you need to convert a hexadecimal number into regular decimal format, simply reverse the process described above. So, for example, if you need to know what the decimal equivalent of 18_{(base 16)} is, all you need to do is remember that the right hand digit is single units, and the next digit to the left is the number of "16s". So 18_{(base 16)} is "1 lot of 16 plus 8 single units". That gives you 16 plus 8, which is 24. If you come across a 3 digit hexadecimal number, the left hand digit is the number of "16x16"s, or "256s".

So 234_(base 16) = ( 2x256 ) + ( 3x16 ) + ( 4x1 ) = 564.

CONTENTS

Introduction

What is HTML?

A Simple HTML Document

Line Breaks & Horizontal Rules

What Next?

Appendix A:
Example Files

Appendix B:
Colour Chart

Appendix C:
Hexadecimal Numbers

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