The hexadecimal numeral system (often called hex) is a base-16 number system.
The word hexadecimal combines the Greek prefix hexa- (“six”) with the Latin word decimal (“ten”), referring to its base of 16. A numeral system’s base tells you how many unique symbols it uses before counting continues in the next place value. Decimal (base-10) uses 10 symbols: 0–9. Hexadecimal (base-16) uses 16 symbols: 0–9 and A–F.
Hexadecimal Numeral System Symbols
Since hexadecimal needs 16 symbols but uses only the numbers 0–9, the letters A through F are used to represent the remaining six values.
| Decimal | Hexadecimal |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 7 | 7 |
| 8 | 8 |
| 9 | 9 |
| 10 | A |
| 11 | B |
| 12 | C |
| 13 | D |
| 14 | E |
| 15 | F |
Beyond F
After F (15), counting continues with 10, just as decimal continues from 9 to 10. In hexadecimal, 10 represents 16 in decimal.
Why Use Hexadecimal?
Computers store all data as binary (0s and 1s). While binary is efficient for computers, long strings of 0s and 1s are difficult for people to read and write. Hexadecimal provides a much more compact way to represent binary. Each hexadecimal digit corresponds to exactly four binary digits (bits).
| Binary | Hexadecimal |
|---|---|
| 1010 | A |
| 1111 | F |
| 11001010 | CA |
Because every hexadecimal digit represents four bits, programmers commonly use hexadecimal when working with memory addresses, machine code, colors, and other binary data.
RGB and Hexadecimal Colors
The RGB color system represents colors by combining red (R), green (G), and blue (B) light.
Each color component is stored in one byte (8 bits). Since 8 bits can represent 256 different values, each component can have a value from 0 to 255. RGB colors are commonly written as (R, G, B), where each number represents the intensity of the red, green, or blue component. Specific colors are represented by changing the component values.
The darkest values are 0, and maximum intensity values are 255:
- (255, 255, 255) is white because all three components are at their maximum value.
- (0, 0, 0) is black because all three components are at their minimum value.
Here are some straightforward (R, G, B) values with components at either maximum or minimum value:
- Red: (255, 0, 0)
- Green: (0, 255, 0)
- Blue: (0, 0, 255)
- Yellow: (255,255,0)
- Magenta: (255,0,255)
- Cyan: (0,255,255)
Hexadecimal Colors
If you’ve worked with HTML, CSS, or looked at colors in a graphics application such as Adobe Photoshop, you’ve probably seen colors represented as a hexadecimal value preceded with a hash (or pound) sign, such as #FFFFFF.
Because each component is stored as one byte, RGB colors are often written in hexadecimal as #RRGGBB, where each pair of hexadecimal digits represents one color component (a single byte is represented by two hexadecimal digits). This is similar to the RGB system (R, G, B) in that the colors are grouped as red, green, and then blue.
- RR = red intensity
- GG = green intensity
- BB = blue intensity
Minimum and Maximum Color Intensity
In RGB and Hexadecimal the minimum value is the same: 0. However, the RGB maximum value of 255 is represented in Hexadecimal as FF (remember that hexadecimal uses the digits 0-9, then A-F).
- 255 RGB = FF hexadecimal (maximum value)
- 0 RGB = 00 hexadecimal (minimum value)
If all values are 0 (minimum intensity) the color will be black #000000. If all values are F (maximum intensity), then the color will be white (#FFFFFF).
| R | R | G | G | B | B | |
| Black | 0 | 0 | 0 | 0 | 0 | 0 |
| White | F | F | F | F | F | F |
Example colors:
- #FF0000 = Red
- #00FF00 = Green
- #0000FF = Blue
Hexadecimal Color Example: Shades of Red
Let’s look at five shades of red.
- First, note that each has the same value for the green and blue components (00). The only difference are the red values.
- Next, remember that the minimum value is 0; values closer to 0 will be darker.
- And finally, keep in mind that the maximum value is F. As values move closer to F they will increase in intensity.
#330000
| RR | GG | BB |
|---|---|---|
| 33 | 00 | 00 |
#660000
| RR | GG | BB |
|---|---|---|
| 66 | 00 | 00 |
#990000
| RR | GG | BB |
|---|---|---|
| 99 | 00 | 00 |
#CC0000
| RR | GG | BB |
|---|---|---|
| CC | 00 | 00 |
#FF0000
| RR | GG | BB |
|---|---|---|
| FF | 00 | 00 |
Gray Shades
Aside from white (#FFFFFF) and black (#000000), if all 6 digits are the same value, the color will be a shade of gray.
Examples:
#222222
| RR | GG | BB |
|---|---|---|
| 22 | 22 | 22 |
#666666
| RR | GG | BB |
|---|---|---|
| 66 | 66 | 66 |
#AAAAAA
| RR | GG | BB |
|---|---|---|
| AA | AA | AA |
#DDDDDD
| RR | GG | BB |
|---|---|---|
| DD | DD | DD |
Shortened Hexadecimal Color Values
If both values in a pair (RR, GG, BB) are the same value, you can shorten the hexadecimal number to a 3-digit hex. For example, white would be #FFF.
However, if the numbers in a pair are not the same you can’t shorten the code and still have the same color. For example, #29A7D9 and #2AD are similar but they are not the same color.
A six-digit hex color can only be shortened to 3 digits when each pair contains identical digits.
- #FFFFFF = #FFF
- #33AA99 = #3A9
- #29A7D9 cannot become #2AD
Lowercase or Uppercase?
Hexadecimal values can be written in either uppercase or lowercase, and both will work the same way (i.e., #FFFFFF and #ffffff). The convention depends on the language, ecosystem, and what the hex value represents.
For most programmers lowercase is preferred for consistency and readability. However, uppercase remains common in embedded systems, hardware documentation, and some legacy codebases.
In this article uppercase is used so that the letters A-F are easier to read.
Hexadecimal Numeral System Prefixes and Suffixes
To avoid confusion with decimal, octal and other numbering systems, hexadecimal numbers are sometimes written with an “h” after the number, or “0x” as a prefix. For example, 63h and 0x63 mean 63 hexadecimal. Additionally, hexadecimal colors use “#” as a prefix (#FFFFFF).
Summary
Hexadecimal Numeral System is a base-16 numbering system that uses the symbols 0–9 and A–F. Each hexadecimal digit represents 16 possible values, while two hexadecimal digits represent one byte (0–255). In web design, RGB colors are written in hexadecimal as #RRGGBB, where higher values produce brighter colors and equal red, green, and blue values create shades of grey.
