Decimal to Octal Converter — Free, Instant, No Signup
- Convert any decimal number to octal in one step — results appear as you type
- See octal, binary, and hex all at once for full cross-reference
- No download, no signup, works in any browser
- Octal to decimal conversion works the same way in reverse
Table of Contents
Converting decimal to octal takes one step with this tool: type your decimal number, select Decimal (Base 10) as the source, and the octal result appears immediately in the output panel. You also see the binary and hex equivalents at the same time, which makes it useful for any base-conversion work.
How to Convert Decimal to Octal
- Open the Number Base Converter
- The default input base is Decimal (Base 10) — leave it set there
- Type your decimal number in the input field
- Read the Octal (Base 8) output from the results panel
- Click Copy to copy the octal value to your clipboard
To convert octal back to decimal: select Octal (Base 8) as the input base and type your octal digits (0–7 only). The decimal equivalent appears instantly.
How Decimal to Octal Conversion Works
The manual method for converting decimal to octal uses repeated division by 8. Divide the decimal number by 8, record the remainder, then divide the quotient again by 8. Continue until the quotient reaches zero. Reading the remainders bottom-to-top gives the octal result.
Example: Convert 156 to octal
- 156 ÷ 8 = 19 remainder 4
- 19 ÷ 8 = 2 remainder 3
- 2 ÷ 8 = 0 remainder 2
- Read remainders bottom-to-top: 234 (octal)
Decimal 156 = Octal 234. You can verify this instantly in the tool — type 156 and the octal output shows 234.
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| Decimal | Octal | Binary | Hex |
|---|---|---|---|
| 8 | 10 | 1000 | 8 |
| 16 | 20 | 10000 | 10 |
| 32 | 40 | 100000 | 20 |
| 64 | 100 | 1000000 | 40 |
| 100 | 144 | 1100100 | 64 |
| 255 | 377 | 11111111 | FF |
| 512 | 1000 | 1000000000 | 200 |
Notice that 64 in decimal is 100 in octal — powers of 8 always produce clean round numbers in octal, just as powers of 10 do in decimal.
Where Octal Is Still Used Today
Octal is most commonly encountered in Unix and Linux file permissions. The chmod command uses octal to represent read (4), write (2), and execute (1) permission bits.
chmod 755— owner can read/write/execute (7), group and others can read/execute (5)chmod 644— owner can read/write (6), group and others can only read (4)chmod 777— everyone has full permissions (not recommended)
Outside of Unix permissions, octal appears in some legacy systems, embedded programming, and computer science courses that teach number systems. It fell out of favor compared to hex because octal digits do not map neatly to binary bytes — three octal digits = 9 bits, which does not line up with 8-bit bytes.
Converting Octal to Decimal (Reverse)
To convert octal to decimal manually, multiply each digit by 8 raised to its positional power and sum the results.
Example: Convert octal 234 to decimal
- 4 × 8⁰ = 4 × 1 = 4
- 3 × 8¹ = 3 × 8 = 24
- 2 × 8² = 2 × 64 = 128
- Sum: 4 + 24 + 128 = 156
With the tool: select Octal (Base 8), type 234, and decimal 156 appears immediately. The converter handles the math so you can focus on what the numbers mean rather than how to convert them.
Convert Decimal to Octal Now
Type any decimal number and get the octal, binary, and hex equivalents all at once — instantly, no signup needed.
Convert Numbers FreeFrequently Asked Questions
What digits are valid in octal?
Octal uses only digits 0 through 7. Digits 8 and 9 do not exist in octal. If you try to enter an 8 or 9 when Octal is selected as the input base, the tool will show an error.
What is 100 in octal?
Decimal 100 equals octal 144. Decimal 64 equals octal 100 — which is where the clean round number falls in base 8.
Does this tool convert octal to binary and hex?
Yes. Select Octal (Base 8) as the input and all four outputs — binary, octal, decimal, hex — update at once. You can see the octal to binary and octal to hex conversions simultaneously.
