Octal to Hex Converter

Octal is older than hex as a programmer’s shorthand. It suited machines with 12-, 18- and 36-bit words, which divide evenly by three. Moving a value to hex means re-cutting the same bits on four-bit boundaries.

1. Write each octal digit as exactly three bits, 0 = 000 through 7 = 111.
2. Join the bits in order.
3. Starting from the right, split them into groups of four and pad the leftmost group with zeros.
4. Read each group as one hex digit and drop a leading 0 if one appears.

Watch the width when the octal value has a leading zero meant as a prefix, as in 0755. The converter treats that zero as an octal marker and says so under the panel, and 0o is removed the same way.

How languages write octal and hex literals

The leading-zero convention from C has caused real bugs: a table of zero-padded numbers such as 010, 020, 030 silently means 8, 16 and 24. Newer languages either require the explicit 0o prefix or treat the bare zero as decimal. Hex has been 0x almost everywhere.

When you copy a mode or a constant between languages, convert the literal rather than the digits: a Python 0o755 pasted into C needs to become 0755 or 0x1ED.

In C string literals, \101 is an octal escape and \x41 a hex one, and both are the byte 65, the letter A. Shells, Perl and many config formats accept the same pair. Converting between them is this page’s method applied to a single byte: 101 is 001 000 001, regrouped as 0100 0001, which is 41.

Octal escapes take up to three digits and stop at the first non-octal character, while hex escapes in C keep consuming hex digits, so "\x41BC" is not A followed by BC. When in doubt, prefer the octal form or split the string.