In short: A number base converter rewrites an integer between binary (base 2), octal (base 8), decimal (base 10), hexadecimal (base 16) and other bases, e.g. 255 = 0xFF = 0b11111111.
About Number Base Converter
Computers think in binary, programmers often write in hexadecimal, Unix permissions use octal, and people count in decimal. Converting between them is a daily task when reading memory addresses, color codes, bit flags or network masks.
This converter keeps all bases in sync: edit any field and the others update instantly. It uses JavaScript’s BigInt, so even 128-bit values convert exactly instead of being rounded the way ordinary floating-point numbers would be. Prefixes like 0x, 0b and 0o, underscores and spaces are accepted, and a negative sign is supported. A custom field covers any base from 2 to 36.
How to use Number Base Converter
- Type a number into whichever field matches the base you have.
- Read the equivalent values in the other fields.
- Use the custom base field for anything from base 2 to 36 (digits then letters a–z).
- Check the info line for bit length and byte count.
Examples
255 decimal = ff hex = 11111111 binary = 377 octal.
Octal 755 = binary 111101101: read/write/execute for the owner, read/execute for everyone else.
Frequently asked questions
How big a number can I convert?
There is no practical limit. BigInt arithmetic is exact for integers with thousands of digits.
Does it support fractions?
No. This tool converts whole numbers. Fractional binary values (like IEEE 754 floats) need a different representation.
How are negative numbers shown?
With a minus sign, e.g. -ff. Two’s-complement representation depends on the bit width your system uses.
Is the input case-sensitive?
No. FF and ff are the same in hexadecimal.
Updated November 2026 · Free, no signup · How we build and test tools