Octal to Decimal Converter

How it is calculated

Each octal digit is multiplied by a power of 8 according to its position, counting from 0 on the right, and the products are added: decimal = Σ dᵢ × 8i. The same value is also shown in hexadecimal with a 0x prefix and upper-case letters. Spaces inside the input are ignored, and leading zeros do nothing, so 0755 and 755 are the same. Only the digits 0 to 7 are accepted: an 8 or 9, a minus sign, a decimal point or a prefix such as 0o gives no result, as does an empty box. The largest value that can be converted is 21 sevens, which equals 9,223,372,036,854,775,807 (2⁶³ − 1); anything longer is refused rather than shown with lost digits. Only whole non-negative numbers are handled.

Common mistakes

• Entering a digit 8 or 9, as in 189 or 98. Octal only has 0 to 7, so the tool gives no result instead of guessing.
• Typing the prefix used in programming languages, such as 0o755 or 0755 with letters. A plain 0755 works, but 0o755 contains the letter o and is rejected.
• Reading the decimal result as the permission digits. 493 is the number of the permission set, not the chmod string; chmod expects 755 itself.
• Entering negative numbers or fractions, such as -17 or 17.5. Only whole, non-negative octal numbers are converted.
• Pasting a value above the limit, such as 1777777777777777777777. The limit is 21 sevens (2⁶³ − 1); larger numbers are rejected.