How to convert decimal to hexadecimal step by step

Short answer

To convert a decimal integer to hexadecimal, divide it repeatedly by 16, record each remainder, and read the remainders from last to first. Remainders 0 through 9 keep their digits; 10, 11, 12, 13, 14, and 15 become A, B, C, D, E, and F.

Example: convert 255 to hexadecimal

Only two divisions are needed:

Reading the remainders from bottom to top gives:

255 decimal = FF hexadecimal

The 0x prefix commonly declares the base, so 0xFF represents the same value. Check it with the IPv4 and number base converter, which uses exact integer arithmetic even for values beyond JavaScript’s safe Number range.

Why division by 16 works

Hexadecimal is a positional base-16 system. Each place has a power-of-16 weight:

FF = 15 × 16¹ + 15 × 16⁰
   = 240 + 15
   = 255

The same process works for every non-negative integer. For example, 4095 produces three remainders of 15, so its result is FFF. Zero is a direct case: decimal 0 is hexadecimal 0.

Common mistakes

• Reading remainders in the order they were produced instead of reversing them.
• Writing decimal 15 as two hexadecimal characters instead of F.
• Treating decimal 10 and hexadecimal 10 as equal: 0x10 is decimal 16.
• Including visual separators as though they were digits.
• Applying two’s complement before choosing a bit width.

A negative mathematical value can keep its sign, such as -26 = -1A. That is not a two’s-complement binary encoding. An 8-, 16-, or 32-bit width must be chosen first because each produces a different pattern; the converter does not guess that width.

Check the conversion

Convert the hexadecimal result back by multiplying each digit by its power of 16. This reverse check catches misplaced remainders and incorrect digits. The ECMAScript specification supports exact BigInt string representations with an explicit radix from 2 through 36 in BigInt.prototype.toString.