Non-octal digits
Digits 8 or 9 are not valid octal.
Fix: Edit the input to use digits 0-7 only.
Octal to Binary Converter
Convert an octal number into its binary form for file permission inspection and low-level register work.
Quick Converter
Use a compact field for small conversion and calculation tools.
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What is Octal to Binary Converter
Last reviewed:
Octal (base 8) represents numbers with digits 0-7 and is still common in Unix file permissions and some legacy systems.
Octal to Binary Converter reads an octal value and returns the equivalent binary string without padding, so you can see each bit involved in file permissions, protocol flags, or register dumps.
Because each octal digit maps to exactly three binary digits, converting back and forth is a simple, reversible mapping that is useful during permission audits and classroom examples.
Why use it
- Inspect Unix file permissions bit-by-bit.
- Audit protocol flags expressed in octal.
- Teach the 3-bit-per-octal-digit mapping visually.
- Debug embedded systems that log values in octal.
- Produce quick binary dumps without a calculator.
Features
- Handles optional 0o prefix
- Compact binary output
- Clear errors for non-octal input
- Instant client-side conversion
- Copy-ready result
How to use Octal to Binary Converter
- Enter the octal. Paste an octal value with or without the 0o prefix.
- Read the bits. The binary representation appears in the output.
- Copy the binary. Use the copy button to move the binary string into your notes.
Example (before/after)
Octal
755
Binary
111101101
Common errors
Expecting 3-bit-per-digit padding
The tool outputs the pure binary number, which may drop leading zeros.
Fix: Pad manually to maintain 3-bit alignment if you need it for readability.
Large values
Very large octal numbers exceed JavaScript's safe integer range.
Fix: Use a BigInt-aware utility for values beyond 2^53 - 1.
FAQ
Is each octal digit 3 bits?
Yes. The underlying mapping is deterministic, though the tool returns the compact binary form without leading zeros.
Does it support the 0o prefix?
Yes. The prefix is stripped before parsing.
Is it done locally?
Yes. No upload.
How do I re-add the leading zeros?
Left-pad the result to a multiple of 3 bits.
What's the maximum value?
Up to 2^53 - 1 due to JS number precision.
How do I reverse it?
Use the Binary to Octal tool.
Related tools
Round-trip between octal and binary, or chain into other base conversions. You can also browse the full Unit Converters category for more options.
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