The conversion of a decimal number to its base 8 equivalent is done by the repeated division method. You simply divide the base 10 number by 8 and extract the remainder. The first remainder will be the LSD, and the last remainder will be the MSD.

Example: Convert 2510 to octal

The division problem will be setup as 2510 ÷ 8
2510 ÷ 8 = 3
2510 – 24 = Remainder 1 -----> 1 (LSD)

3 ÷ 8 = 0
3 – 0 = Remainder 3 -----> 3 (MSD)

Now, write the number from MSD to LSD as 318.

This same process can be used regardless of the size of the decimal. Here is an example of a larger decimal.

Example: Convert 25810 to octal.

The division problem will be setup as 25810 ÷ 8
25810 ÷ 8 = 32
18 – 16 = Remainder 2 -----> 2 (LSD)

32 ÷ 8 = 4
32 – 32 = Remainder 0 -----> 0

4 ÷ 8 = 0
4 – 0 = Remainder 4 -----> 4 (MSD)

Now, write the number from MSD to LSD. You should end up with 4028.

To convert a decimal fraction to octal, you must multiply the fraction by 8. Then, you need to extract the number(s) that appear to the left of the decimal point. The first number that is extracted will be the MSD and will follow the decimal point. The last number that is extracted will be the LSD. Continue to desired accuracy. This type of problem may result in results containing a mixed decimal number, which requires the whole number and the fraction to become split in order to achieve its equivalent octal conversion.
Example: Convert 0.17510 to octal.

The multiplication problem will be setup as

.017510
× 8
0.1400 -----> 0 (MSD)

.1400
× 8
1.1200 -----> 1

.1200
× 8
0.9600 -----> 0

.9600
× 8
7.6800 -----> 7

.6800
× 8
5.4400 -----> 5

.4400
× 8
3.5200 -----> 3

.5200
× 8
4.1600 -----> 4

.1600
× 8
1.2800 -----> 1 (LSD)

Writing from MSD to LSD, you should end with .010753418.