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Decimal to Octal

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 remainders. The first remainder will be the LSD, and the last remainder will be the MSD.

Look at the following example. To convert 15₁₀ to octal, set up the problem for division:

Since 8 goes into 15 one time with a 7 remainder, 7 then is the LSD. Next divide 8 into the quotient (1). The result is a 0 quotient with a 1 remainder. The 1 is the MSD:

Now write out the number from MSD to LSD as shown:

17₈

The same process is used regardless of the size of the decimal number. Naturally, more divisions are needed for larger numbers, as in the following example:

Convert 264₁₀ to octal:

By rewriting the solution, you find that the octal equivalent of 264₁₀ is as follows:

410₈

To convert a decimal fraction to octal, multiply the fraction by 8. Extract everything that appears to the left of the radix point. The first number extracted will be the MSD and will follow the radix point. The last number extracted will be the LSD.

Convert 0.05₁₀ to octal:

Write the solution from MSD to LSD:

.03146₈

You can carry the conversion out to as many places as needed, but usually four or five places are enough.

To convert a mixed decimal number to its octal equivalent, split the number into whole and fractional portions and solve as shown below:

Convert 105.589₁₀ to octal:

Combine the portions into a mixed number:

151.4554₈

Convert the following decimal numbers to octal:

Q.54 7₁₀.
Q.55 43₁₀ .
Q.56 499₁₀.
Q.57 0.951₁₀ (four places).
Q.58 0.004₁₀ (five places).
Q.59 252.17₁₀ (three places).