Konwerter baz liczbowych

What the number base converter does

This tool converts a whole number between the four bases that show up constantly in computing: binary (base 2), octal (base 8), decimal (base 10) and hexadecimal (base 16). You type a value, tell it which base that value is written in, and it shows you the number in all four bases at once. It is the utility you reach for when the same quantity keeps appearing in different notations and you need to move between them: reading a hex byte value from a file or colour code, working out what an octal file-permission like 755 means in bits, decoding a bitmask of feature flags, checking a memory address, or just seeing the binary shape of a decimal number while learning how positional notation works.

How positional bases actually work

Every one of these systems is positional: each digit is worth its face value multiplied by the base raised to the digit’s position. In decimal, 255 means 2×10² + 5×10¹ + 5×10⁰. The same quantity is FF in hexadecimal (15×16 + 15), 377 in octal, and 11111111 in binary. Hexadecimal earns its popularity because 16 is 2⁴, so each hex digit maps exactly onto four bits (a “nibble”) and every byte is two clean hex digits — which is why colours, hashes and byte dumps are written in hex. Octal groups bits in threes, the reason Unix file permissions (read=4, write=2, execute=1) are written as octal digits. The tool uses the digits 0–9 and then the letters a–f for the values ten to fifteen in hex; it is case-insensitive on input and prints hex in uppercase.

Big-integer precision, and why that matters

A quiet but important detail: this converter is built on JavaScript’s BigInt, so it has arbitrary precision. A naive converter using parseInt and normal numbers silently loses accuracy for values above 2⁵³ (about 9 quadrillion), quietly rounding the low digits — disastrous when the number is a 64-bit identifier, a 128-bit UUID as a number, a 256-bit hash, or a full IPv6 address. Because this tool carries every digit exactly, you can convert values of that size without corruption.

• Decimal 3232235777 is hex C0A80101, which is the packed form of the IPv4 address 192.168.1.1 — the same trick our IP check and address tools rely on to store addresses as integers.
• Octal 755 is binary 111101101: rwxr-xr-x file permissions, one triplet of bits per user class.
• Hex FF is decimal 255 and binary 11111111 — one full byte, the maximum value of a single colour channel.
• You may include _ or spaces as visual separators in the input; they are ignored, so 1010_1100 parses fine.

Gotchas to keep in mind

Two things trip people up. First, you must tell the tool the base of your input, because a string like 101 is a valid number in every base and means something different in each — five in binary, sixty-five in octal, one hundred and one in decimal, and two hundred and fifty-seven in hex. Second, this handles whole numbers only: there is no fractional or floating-point support, and a leading minus sign is treated as ordinary signed magnitude, not as two’s-complement binary, so it does not model how a negative number is actually stored in a fixed-width register. Any digit that is out of range for the chosen base — a 2 in binary, or a G in hex — is reported as an error rather than being guessed.

Runs entirely on your device

The conversion is done locally in your browser with client-side JavaScript. The numbers you enter — which might be an internal identifier, an address, or a value pulled from a private system — never leave your machine, are not uploaded, and are not logged anywhere. Everything is computed on your own device, so even sensitive values are safe to paste, and closing the tab leaves no trace behind.