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Hazuu Tools

Octal to Decimal Converter

Translate base-8 octal numbers into their standard base-10 decimal equivalents — paste, convert, and copy instantly.

Octal Input
Decimal Output
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About Octal to Decimal Converter

Octal to Decimal Converter translates base-8 numbers into their standard base-10 equivalents instantly. You type or paste one or more octal values — digits 0 through 7, optionally prefixed with 0o — and the tool outputs the corresponding decimal integer on each line. It also accepts space- or newline-separated batches, so you can convert a whole list in one pass.

The most common reason to reach for this converter is Unix and Linux file permissions. When chmod 755 or chmod 644 appears in a script or tutorial, the three-digit octal code maps directly to the read/write/execute bits for owner, group, and others. Converting 755 gives 493 and 644 gives 420, which are the raw permission masks stored by the kernel. Beyond permissions, octal literals appear in older C source code, PDP-11 assembly, network device configuration, and certain embedded-systems registers — any context where grouping bits in threes was historically convenient.

All arithmetic runs entirely in your browser using JavaScript BigInt, so arbitrarily large octal numbers convert without overflow errors. Nothing is sent to a server, no account is required, and there are no usage limits.

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Key Features

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Batch conversion

Separate multiple octal values with spaces or newlines and convert the entire list at once. Each value gets its own decimal result on a new output line.

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BigInt precision

Uses JavaScript BigInt internally, so numbers far beyond the 53-bit safe integer limit convert correctly without rounding or overflow.

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Accepts 0o prefix

Input like 0o755 or 0O644 is handled automatically — the prefix is stripped before conversion so you can paste directly from source code.

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Clear validation errors

If a value contains a digit outside 0-7 (such as 8 or 9), the tool shows a specific error message identifying the offending token rather than silently returning a wrong answer.

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100% client-side

Every conversion happens in your browser. No data leaves your machine, making it safe to paste internal configuration values or permission sets from private servers.

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One-click copy

Copy all decimal results to the clipboard with a single button and paste them straight into your terminal, script, or spreadsheet.

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How to Use

01

Type or Paste Octal

Enter one or more octal numbers in the left pane. You can separate multiple values with spaces or newlines. The 0o prefix is optional.

02

Click Convert to Decimal

Press the Convert button. Each valid octal number is converted to its decimal equivalent and displayed on a matching line in the right pane.

03

Copy the Result

Use the copy button to grab all decimal values at once and paste them wherever you need them.

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Example

Converting three Unix chmod permission values — 755, 644, and 777 — shows the decimal integers the kernel stores for each permission mask.

Octal input
755
644
777
Decimal output
493
420
511
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Common Use Cases

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    Decoding Unix file permissions

    chmod values like 755 or 644 are octal shorthand for the nine permission bits. Converting to decimal (493 and 420) lets you cross-reference kernel documentation or pass the raw mask to system calls that expect a decimal integer.

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    Reading legacy C and embedded code

    C integer literals starting with 0 are octal by convention. When auditing older codebases or embedded firmware, converting octal constants to decimal makes their actual numeric values immediately readable.

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    Studying number systems in coursework

    Students learning positional notation need to verify manual base-8 to base-10 calculations. This tool converts instantly and shows the correct decimal so you can check your long-form working.

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    Working with PDP-11 and retro computing

    PDP-11 and many DEC systems represented memory addresses and instruction opcodes in octal. Converting archived octal addresses to decimal is often necessary when comparing them with modern disassembler output.

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    Scripting and automation sanity checks

    Shell scripts that set permissions programmatically sometimes mix octal literals and decimal constants. Quickly verify that your octal constant equals the expected decimal value before committing the change.

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Frequently Asked Questions

What is octal to decimal conversion? expand_more
Octal (base 8) uses digits 0-7. To convert to decimal (base 10), each digit is multiplied by 8 raised to its positional power and the products are summed. For example, octal 755 = 7×64 + 5×8 + 5×1 = 448 + 40 + 5 = 493.
What does chmod 755 mean in decimal? expand_more
The octal value 755 converts to decimal 493. In terms of file permissions, 755 means the owner can read, write, and execute (7), while the group and others can read and execute but not write (5 each). The decimal 493 is the raw integer representation of those nine permission bits.
Why do Unix permissions use octal instead of decimal? expand_more
Each permission group (owner, group, others) has exactly three bits: read, write, and execute. One octal digit represents exactly three bits, so a three-digit octal number maps cleanly to all nine permission bits. Decimal does not have this clean alignment with groups of three bits.
How is this tool different from hex to decimal conversion? expand_more
Hexadecimal (base 16) uses digits 0-9 and letters A-F, and one hex digit represents four bits. Octal (base 8) uses only digits 0-7, and one octal digit represents three bits. The two systems are used in different contexts — hex is standard for memory addresses, color codes, and network protocols, while octal is most common in Unix permissions and older assembly code. Use the Hex to Decimal tool when working with hex values; use this tool specifically for octal input.
How is this tool different from binary to decimal conversion? expand_more
Binary to Decimal converts base-2 values made up of only 0s and 1s. This tool converts base-8 values. You would use the Binary to Decimal converter when you already have a string of bits; use this converter when you have a compact octal representation that groups those bits into single digits.
Can I convert multiple octal numbers at once? expand_more
Yes. Enter one octal value per line, or separate values with spaces, and the tool converts each one individually. The results appear in the output pane with one decimal number per line, in the same order as your input.
Does the tool handle the 0o prefix used in JavaScript and Python? expand_more
Yes. Input like 0o755 or 0O644 is recognised automatically. The prefix is stripped before the conversion so you can paste octal literals directly from source code without editing them first.
Is there a limit on how large the octal number can be? expand_more
No practical limit. The tool uses JavaScript BigInt, which handles integers of arbitrary size. Standard JavaScript numbers are only safe up to 2^53 - 1, but BigInt removes that ceiling, so very large octal values used in cryptographic or low-level programming contexts convert accurately.