Is anything sent to a server?

No. Conversion is arithmetic performed in your browser. Nothing is transmitted or stored.

Why does a very large number fail?

JavaScript represents integers exactly only up to 2^53 − 1. Beyond that, digits would silently become wrong, so the tool refuses rather than showing you a plausible but incorrect answer.

Can it handle negative numbers or decimals?

Negative integers work. Fractional values do not — base conversion of fractions has its own rounding rules and is a different problem.

Number Base Converter

Runs in your browser

Convert a number between binary, octal, decimal and hexadecimal — all four at once, in your browser.

Value

Input base

Binary (2)0b11111111
Octal (8)0o377
Decimal (10)255
Hexadecimal (16)0xFF

About this tool

Different bases suit different jobs, which is why one value ends up written four ways. Hexadecimal compresses bytes into two readable characters, so it dominates colours, memory addresses and hashes. Binary makes bit-level flags and permission masks legible. Octal survives mainly in Unix file modes. Converting between them is mechanical, and doing it in your head is a reliable way to introduce an off-by-one.

How to use

Type a value and tell the converter which base it is in.
Prefixes like 0x, 0b and 0o are accepted and stripped automatically.
Copy whichever representation you need.

When to use this tool

Turning a hex colour channel into decimal.
Reading a Unix permission mask in binary.
Converting a hex memory address or opcode while debugging.
Checking a bitmask value against its flags.

Tips

Hex digits A–F are case-insensitive here; output is uppercase by convention.
Underscores and spaces are ignored, so 1010_1010 works.
For text rather than numbers, use Text to ASCII instead.

Limitations

Limited to integers JavaScript can represent exactly (up to 2^53 - 1).

FAQ

Is anything sent to a server?: No. Conversion is arithmetic performed in your browser. Nothing is transmitted or stored.
Why does a very large number fail?: JavaScript represents integers exactly only up to 2^53 − 1. Beyond that, digits would silently become wrong, so the tool refuses rather than showing you a plausible but incorrect answer.
Can it handle negative numbers or decimals?: Negative integers work. Fractional values do not — base conversion of fractions has its own rounding rules and is a different problem.