Convert Decimal to Hex

A base-16 number system using the 16 digits 0-9 and a-f (or A-F). Each hex digit encodes exactly 4 bits, so two hex digits = one byte. That’s why hex is the standard for byte-level representation in debuggers, memory dumps, colour codes, and cryptographic hashes.

Because 255 in base 10 fills all 8 bits of one byte, and the largest 2-digit hex value is ff = 15 × 16 + 15 = 255. So 255 is the maximum unsigned byte and ff is its hex form – one of the reasons hex is so useful for byte-level work.

Default is two’s complement, matching how CPUs store signed integers. In 8-bit two’s complement, -5 is fb (because 256 − 5 = 251 = fb). Sign-magnitude mode instead prints -5 with a literal minus sign – useful for human-readable output but not for machine representation.

Because the tool rounds up to the next multiple of 4 bits (one hex nibble). Decimal 200 needs 8 bits of binary, so 2 hex digits (c8). Decimal 1000 needs 10 bits of binary, rounded up to 12 bits, so 3 hex digits (3e8). This keeps the output nibble-aligned.

0x is the C convention adopted by almost every modern language (Python, JavaScript, Rust, Java 7+, C23). 0X is the same but uppercase – allowed in C but less common. # is the CSS colour prefix (#ff0000) and was used historically in some assemblers. Pick based on where you’ll paste the result.

You get a specific error naming the limit: “overflow: 256 exceeds unsigned 8-bit max ff (255)” or “overflow: 128 exceeds signed 8-bit range [-128, 127]”. The tool refuses to silently truncate – overflows usually indicate a real bug in the caller’s math.

No practical upper bound. The tool uses BigInt, so 2¹²⁸, 2¹⁰⁰⁰, or a 200-digit decimal all convert exactly. JavaScript’s Number.toString(16) would quietly round past 2⁵³ ≈ 16 decimal digits, but BigInt avoids that.

No – integer only. 0.5 in hex floating-point notation would be 0x1p-1 (IEEE 754-style), which is a different encoding. Use a float-to-hex tool for fractional values.

Enter 16711680 (the RGB decimal for pure red), pick 24-bit width and # prefix, and you get #ff0000. For alpha: pick 32-bit width. This tool isn’t a CSS colour picker but makes the math painless when you have a raw RGB integer.

Yes. All arithmetic runs in your browser via JavaScript + BigInt. No upload, no tracking, no account. Load the page once and it works offline indefinitely.