Hexadecimal notation (base 16) is ubiquitous in computing: CSS color codes (#FF5733), memory addresses, register values, MD5/SHA hashes and network protocols. Knowing how to convert between hexadecimal and decimal is an essential skill for developers and IT professionals.
Base 16 uses digits 0–9 and letters A–F (A=10, B=11, C=12, D=13, E=14, F=15). Each hexadecimal digit represents 4 bits (a half-byte, called a nibble). Two hex digits therefore represent a complete byte (0–255 in decimal). To convert hex → decimal, multiply each digit by the corresponding power of 16 at its position. For decimal → hex, repeatedly divide by 16 and read remainders upward.
📐 Formula
Hex → Decimal: d = Σ(digit × 16^position) | Decimal → Hex: divide by 16, read remainders from bottom to top
📊 Reference table
| Hexadecimal | Decimal | Binary | Common use |
|---|---|---|---|
| 0x00 | 0 | 00000000 | Null value |
| 0x0F | 15 | 00001111 | Max low nibble |
| 0xFF | 255 | 11111111 | Max byte, CSS opacity |
| 0x1F4 | 500 | 111110100 | Generic value |
| 0xFFFF | 65,535 | 16 bits all 1 | Max network port |
| #FFFFFF | R:255 G:255 B:255 | — | White in CSS |
| #FF0000 | R:255 G:0 B:0 | — | Red in CSS |
💡 Practical examples
Example 1: decode a CSS color #3A7BD5
R = 0x3A = 3×16+10 = 58. G = 0x7B = 7×16+11 = 123. B = 0xD5 = 13×16+5 = 213. rgb(58, 123, 213) — a medium blue.
Example 2: convert 255 to hexadecimal
255 ÷ 16 = 15 remainder 15 (F). 15 ÷ 16 = 0 remainder 15 (F). Read from bottom to top: FF. 255 decimal = 0xFF.
Example 3: memory address 0x7FFF0000
0x7FFF0000 = 7×16⁷ + F×16⁶ + F×16⁵ + F×16⁴ + 0×... = 2,147,418,112 in decimal. 64-bit memory addresses are far more readable in hex than decimal.