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Number Base Converter

Convert a signed whole number between bases 2 and 36.

Inputs stay on your device No sign-up Free to use
How this works

The tool runs in this browser. Your file or text is not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.

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Showing an example. Edit to see your own.

Digits in the source base. A minus sign is allowed, and grouping spaces, underscores or apostrophes are ignored. Fractions are not converted.

Set the base before typing, so a leading 0b, 0o or 0x is checked against it instead of guessed.

Letter digits are written in uppercase, so decimal 255 is FF in hexadecimal. Lowercase input is accepted as well.

Processed in your browser. Your inputs stay on this device.

How to use Number Base Converter

  1. Type the Number to convert.
  2. Set The number above is written in to your current base.
  3. Tick the bases you want back, such as Show binary (base 2).
  4. The Base, Value and Digits table updates as you change the number.

Example: Number Base Converter

Write decimal 255 in binary, octal and hexadecimal.

You add
Number to convert 255, written in Decimal (base 10), with binary, octal, decimal and hexadecimal ticked.
You get
Base 2: 11111111 (8 digits). Base 8: 377 (3 digits). Base 10: 255. Base 16: FF (2 digits). In hexadecimal F stands for fifteen, so FF is fifteen sixteens plus fifteen.

Options

The number above is written in
Set the source base before you type, so a leading 0b, 0o or 0x is checked against your choice instead of guessed.
Grouping separators
Spaces, underscores and apostrophes inside a long number are ignored, which helps with a pasted value that was already grouped. A separator at the start or end is reported.

Supported inputs and limits

Bases 2 to 36. Each entered number can hold up to 1,000 digits and a result is refused past 4,000 digits. Only whole signed integers are converted, so a decimal point or fraction is rejected and two's-complement patterns are not interpreted. Letter digits are written in uppercase, so 255 is FF, while lowercase input is accepted. A leading 0b, 0o or 0x is allowed only when it names the base you selected.

Where your input is processed

This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.

Place value is what changes

The value does not move when its spelling changes. In decimal, 255 is 2 hundreds, 5 tens and 5 ones. In hexadecimal it is FF, where the first F is worth fifteen sixteens and the second is fifteen. The page shows that positional breakdown for the number you enter.

Why exact integers matter

Floating-point numbers hold a fixed number of significant digits, so a long identifier can gain a rounded tail. Values here stay exact from input to output, which is why a 17-digit input converts without altering its last digit.

Questions about Number Base Converter

Why is my 0x value rejected?

The prefix must name the base you selected. 0x means base 16, so it fails when the field is set to base 2 or 10.

Can I convert 1.5?

No, this page converts whole numbers only. Enter the value as a fraction such as 3/2 and use the Fraction Calculator.

Why does a 16-digit number keep its last digit?

The digits are held as an exact integer. A JavaScript Number would round anything above 9,007,199,254,740,991.

Does it understand two's complement?

No. A minus sign is allowed, but this page does not fit a number into a bit width or read a two's-complement pattern.

Project manager: Tony Hines · Content updated 29 September 2026 · Report a problem

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