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Quick reference (0–15)
Why 8 and 16 and not 100
Octal and hexadecimal exist because they line up neatly with binary: one octal digit is exactly three bits, one hex digit exactly four. That is why a byte is two hex digits and why hex is the everyday way to write memory addresses and colours.
Reading binary in groups of four
The binary result is shown in groups of four bits. Each group maps to one hex digit, so 1010 1111 reads straight off as AF. Once you see the pairing, converting by eye stops being work.
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Frequently asked questions
Q. Why do colours use hex?
A colour is three bytes — red, green, blue. Each byte is exactly two hex digits, so #1A2B3C packs all three into six characters with no ambiguity about where one ends.
Q. Are hex letters case sensitive?
No. A–F and a–f mean the same digits. Enter either; the result is shown in uppercase.
Q. Can I convert negative numbers?
Negative values are accepted in decimal. Binary, octal and hex here represent magnitudes, so enter the digits without a sign.