Number Base Converter — Binary, Octal, Decimal, Hex

What this Number Base Converter does

This English-language number base calculator shows binary (base 2), octal (base 8), decimal (base 10), and hexadecimal (base 16) side by side and keeps all four in sync as you type. Most base converter online tools force you to pick a source and a target; here every field is editable — change any one and the other three follow immediately. Paste values with prefixes like 0b, 0o, or 0x and they are stripped automatically. The tool also reports bit-length and byte-length, so you can size data structures at a glance without mental arithmetic. As defined in encoding standards such as RFC 4648, precise radix representation matters in data interchange — getting it wrong at the bit level causes real bugs. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs.

Features

Live four-way editing. Type or paste into any of the four base fields and the other three update instantly — no submit button needed for conversion.
Prefix-aware input. Paste values prefixed with 0b001010010, 0o755, or 0xFF and the tool strips the prefix and parses correctly. Most other converters reject prefixed input.
Bit-length and byte-length display. Alongside each converted value you see how many bits and bytes the number occupies, useful for sizing fields in structs, network packets, or file formats.
Full binary–octal–decimal–hex table view. All four representations appear simultaneously, giving you the complete binary decimal octal hexadecimal picture without toggling between separate calculators.
Privacy-first, no install. Runs entirely in your browser. No account, no server round-trip, no usage logs — the conversion logic never touches a remote host. If you also work with encoded text, the [Base64 encoder & decoder](/en/base64/) follows the same privacy model.
One-click copy per field. Each output field has its own Copy button so you can grab exactly the representation you need — hex constant, binary literal, or decimal value — without selecting text manually.

How to use the Number Base Converter

Enter any integer in whichever base you already know and read off the others immediately.

Enter your number. Type a value into whichever field matches your input base — decimal, hex, octal, or binary. You can include a prefix: 0xFF, 0b1101, or 0o17 all parse correctly.
Read the other bases. The remaining three fields update in real time. For example, typing 255 in decimal immediately shows FF in hex, 377 in octal, and 11111111 in binary.
Check bit and byte length. Glance at the bit-length indicator to confirm the value fits your target type — handy when working with 8-bit, 16-bit, or 32-bit fields.
Copy the result you need. Click the Copy button next to any field to put that specific representation on your clipboard, ready to paste into source code, a config file, or a spreadsheet.

Common use cases

Reading memory addresses. Paste a raw pointer like 0x7FFE0000 from a debugger in Seattle or Austin and immediately see the decimal equivalent and bit-width to verify it fits a 32-bit address space.
Translating bitmasks and flags. Convert a hex constant such as 0x0F to binary 00001111 to understand exactly which bits a mask affects — essential when reading or writing bitfield registers.
Decoding Unix file permissions. Enter 0o755 to see 111 101 101 in binary, which maps directly to rwxr-xr-x. The octal conversion calculator view makes permission logic visually obvious.
Networking and protocol work. Convert port numbers, MTU sizes, or IP address octets between decimal and hex on the fly. Pair this with the [color converter](/en/color-converter/) when you also need to decode RGB hex values.
CS coursework and interview prep. Work through radix conversion problems and verify answers instantly. The side-by-side decimal binary octal hexadecimal table serves as a live reference while you study.

Frequently asked questions

Does this tool send my numbers to a server?

No. Every conversion runs in your browser using JavaScript. No value you enter is transmitted anywhere — there are no server logs and no analytics that capture input data.

Why does a leading zero change a number's meaning in C or Python?

In C-family languages a leading zero signals octal (base 8), so 010 equals 8 in decimal, not 10. Python 3 made this explicit by requiring the 0o prefix for octal literals. The octal translator here accepts both forms and shows you the decimal value immediately so you can catch this pitfall before it ships.

What is the largest number this base converter calculator can handle?

The tool uses standard JavaScript numbers, which are safe up to 2^53 − 1 (9,007,199,254,740,991). Beyond that, floating-point precision limits kick in and results may be incorrect. For cryptographic keys or very large hex values, use a BigInt-aware environment instead.

Why does 0xFF look so different in binary?

0xFF equals 255 in decimal and 11111111 in binary — the same quantity expressed with different symbol sets. Hex is compact because each hex digit maps to exactly four bits, so two hex digits always represent one byte. The bit-length display in this tool makes that mapping explicit.

How is this different from a standard number base conversion calculator?

Most tools give you a source-base picker and a target-base picker. This one treats all four fields as equal inputs — edit any of them and the rest update live. It also accepts prefixed values like 0b001010010 that other converters reject, and shows bit and byte length alongside every result.

Is there a way to encode the converted value as Base64 or in a URL?

Not directly from this tool, but the [Base64 encoder & decoder](/en/base64/) and [URL encoder & decoder](/en/url-encoder/) on this site handle those tasks. Convert your number here first, then paste the result into whichever encoder you need.