Explainer1 min readUpdated June 25, 2026

What is hexadecimal?

Short answer

Hexadecimal (hex) is a base-16 number system using the digits 0-9 and the letters A-F. It is popular in computing because each hex digit maps neatly to exactly four binary bits, making long binary values short and readable.

Counting in base 16

Decimal uses ten digits, 0-9. Hexadecimal uses sixteen, so after 9 it continues with A (10), B (11), C (12), D (13), E (14), and F (15). The value FF therefore means 15 times 16 plus 15, which is 255.

hex  A     =  decimal 10  =  binary 1010
hex  F     =  decimal 15  =  binary 1111
hex  FF    =  decimal 255 =  binary 1111 1111

One hex digit = four bits

Why computing loves hex

A byte is eight bits, which is exactly two hex digits. That clean mapping makes hex a compact shorthand for binary: a 32-bit value fits in eight hex digits instead of a wall of ones and zeros. Hex usually appears with a 0x prefix, as in 0x1F.

Where you see it

CSS and design colors, such as #2563EB, which is three bytes of red, green, and blue
Memory addresses and byte dumps in debuggers
Character codes and Unicode code points, such as U+1F600
Hashes and identifiers written as long hex strings

Try it: Base ConverterConvert between binary, decimal, hexadecimal, and other bases locally.Open tool

References

Questions

Why does hex use letters?

Base 16 needs sixteen distinct digits, but we only have ten numeric ones. The letters A through F fill the gap, representing the values 10 through 15.

What does the 0x prefix mean?

The 0x prefix is a convention that marks the following digits as hexadecimal, so 0x10 (sixteen) is not confused with the decimal number 10.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.