Number Base Converter: Hex, Binary, Octal, Decimal

How it works

A bit pattern has no sign until you pick a width. 0xFF is 255 as an unsigned byte and −1 as a signed one, because signed integers use two’s complement: the top bit counts as negative. The table shows every input at 8, 16, 32, and 64 bits, read both ways:

Bits	As int8 / int32	As uint8 / uint32
0xFF	−1	255
0x80	−128	128
0xFFFFFFFF	−1	4,294,967,295

A value that doesn’t fit wraps around when it’s stored: 300 in a uint8 becomes 44 (300 − 256). That’s what the “overflows: wraps” rows show. The same rule is behind the year-2038 problem: a signed 32-bit Unix timestamp tops out at 2,147,483,647 seconds and wraps to a negative number.

• Big numbers are exact. Everything runs on JavaScript BigInt, so a 64-bit ID or a 300-digit number converts digit for digit. A plain JS Number can’t do that past 2^53 − 1 (9,007,199,254,740,991): JSON.parse turns 9007199254740993 into 9007199254740992 without an error. That’s how 64-bit database IDs get corrupted in a browser, and why APIs like X’s send IDs as strings too. When your number is past that limit, the result shows what JS would turn it into.
• A leading zero isn’t octal here. In C, Python 2, chmod, and older JavaScript, 0755 means octal 493. This tool reads a bare 0755 as decimal and adds a note saying so. Write 0o755 or pick Oct to mean octal.
• Byte order. Network protocols and most file formats store the most significant byte first (big-endian); x86 and ARM memory stores the least significant first (little-endian). Both orders are listed, so you can match the value against a hex dump either way.
• Prefixes 0x, 0o, and 0b are detected in Auto mode, and _, spaces, and thousands commas are ignored, so 0b1111_0000 and 1,000,000 both work.

Whole numbers only. Fractions generally have no exact binary form (0.1 repeats forever in base 2), and how floats are laid out in memory is a different topic. Runs entirely in your browser; nothing you type is uploaded or stored.