What is a number base converter?
Computers work in binary, programming leans on hexadecimal (colors, memory addresses, Unicode code points), and people think in decimal. This number base converter converts between binary, octal, decimal and hex live — edit any field and the other three update instantly — and it can also turn text into binary or hex and back. Everything runs locally in your browser.
How to use
- In the "base conversion" area, type a number into any field; the other bases sync instantly.
- For text, use the "Text ⇄ Binary / Hex" area: paste text to get binary and hex, or paste binary or hex to decode it back to text.
- Copy any result in one click.
Common use cases
- Turn a hex value from a log or memory dump into decimal.
- Make sense of bit masks, flags and permission values.
- Convert a string to its byte sequence for debugging. Need Base64? Use the Base64 tool; for color codes, the color converter.
Why does binary-to-text come out as garbage?
There are two separate areas here — don't mix them up. The "base conversion" block above rewrites a single number in different bases (seeing 255 as ff); the "Text ⇄ Binary" block below splits text into bytes via UTF-8. Paste binary that was meant as a number into the text field and you'll usually get garbage — its bits aren't necessarily a valid UTF-8 byte sequence. The rule for decoding text is: the bit count must be a multiple of 8 (one byte per 8 bits) and form valid UTF-8. Also note that a Chinese character is usually 3 bytes (24 bits), not one, and emoji are more — so "text to binary" comes out longer than you might expect.
Which numbers are worth memorising?
Boundary values are more useful than random ones. Straight out of this page: 255 is ff in hex and 11111111 in binary — the ceiling of one byte, eight ones. Add one and you cross it: 256 is 100 and 100000000. And 4095 is fff, which shows exactly why one hex digit maps to four bits; 65535 is ffff, the ceiling of two bytes. Learn those four and most hex stops needing a lookup.