Octal to decimal converter
Enter a octal number and get its decimal value instantly, plus the other bases and the step-by-step working. Handles huge numbers, negatives and fractions.
Working for 7558
Multiply each digit by its place value
- 7 × 8^27 × 64= 448
- 5 × 8^15 × 8= 40
- 5 × 8^05 × 1= 5
Add them up: 493 in decimal.
How to convert octal to decimal
- Multiply each digit by 8 raised to its position from the right (1, 8, 64, 512…).
- Add the results.
- 157 = 1 × 64 + 5 × 8 + 7 = 111.
Octal survives mainly in Unix file permissions (chmod 755), in some older systems, and in C/Python literals such as 0o755. Decimal is the base people count in, so it is the usual starting or ending point when you need a value a human can check.
Related conversions
Binary to decimal · Octal to binary · Octal to hex · Decimal to octal · Hex to decimal · any base 2–36 · signed (two's complement)
Questions people ask
How do you convert octal to decimal?
Multiply each digit by 8 raised to its position from the right (1, 8, 64, 512…). Add the results. 157 = 1 × 64 + 5 × 8 + 7 = 111.
What is 755 in decimal?
755 in octal (base 8) is 493 in decimal (base 10).
Does it handle negative numbers and fractions?
Yes. A leading minus sign is kept, and digits after a point are converted too. Some fractions that end in one base repeat forever in another (0.1 in decimal is 0.000110011… in binary), so the result is cut at 24 digits and marked as repeating.
Is there a size limit?
No practical one. The converter uses arbitrary-precision integers (JavaScript BigInt), so 64-bit, 128-bit and longer values convert exactly, without rounding.