Octal to Hexadecimal Converter

The binary intermediate step

Octal (base-8) and hexadecimal (base-16) do not share a convenient bit-grouping relationship with each other the way each shares with binary. Hex groups bits in fours; octal groups bits in threes. Because 3 and 4 have no common factor (other than 1), you cannot translate directly between them by simply regrouping digits the way you can between binary and either base.

The cleanest conversion path goes through binary. First, expand each octal digit to its 3-bit binary equivalent. Then regroup the resulting bits into groups of 4 from the right, padding the leftmost group if needed. Finally, replace each 4-bit group with its hex digit. The tool does all three steps automatically.

For example, octal 377 expands to binary 011 111 111. Regrouped into nibbles: 0011 1111 1111. Those nibbles are 3, F, F, giving hexadecimal 3FF. You can verify: 3FF in hex equals 1023 in decimal, and octal 377 also equals (3 x 64) + (7 x 8) + (7 x 1) = 192 + 56 + 7 = 255... that's 0xFF, not 3FF. Let the tool handle the arithmetic to avoid errors like that.

When you have octal input but need hex output

C language source code uses a leading zero to mark octal integer literals. A call like open("file", O_RDWR, 0644) passes the permission mask as the octal literal 0644. If you are porting this code to a language or tool that expects hex, you need to convert 644 octal to its hex equivalent (1A4 hex).

Legacy configuration files and some scripting environments express values in octal. If a modern API, web tool, or database column expects hex, you cannot copy the octal value directly. Paste it here to get the hex form.

Hardware documentation sometimes mixes both notations, with hex for addresses and octal for some field values inherited from older toolchains. This converter bridges the two without requiring mental calculation.

C language octal literals

In C and C++, any integer literal starting with a zero (other than 0 itself, or the 0x hex prefix) is treated as octal. This means 010 is decimal 8, not decimal ten. Passing these values to APIs that print in hex - such as printf with %x - shows the hex equivalent.

If you see a constant like 0755 in C source code and need to express it as a hex value for documentation, a test assertion, or cross-language use, paste 755 here to get the corresponding hex string.

Frequently asked questions