CBSE Class 11 | Number System 5

Octal to Decimal conversion

How to convert octal to decimal:

For octal number with n digits:

dn-1 … d3 d2 d1 d0

The decimal number is equal to the sum of octal digits (dn) times their power of 8 (8n):

decimal = d0×80 + d1×81 + d2×82 + …

Example:1

Find the decimal value of 31 octal:

Convert (31)8 to (n)10

Octal Value 3 1
Power of 8 81 80

=> 3*81 + 1*80
=> 24 + 1
=> 25

So we have

(31)8 = (25)10

Example:2

Find the decimal value of 47 octal:

Convert (47)8 to (n)10

Octal Value 4 7
Power of 8 81 80

=> 4*81 + 7*80
=> 32 + 7
=> 39

So we have

(47)8 = (39)10

Example:3

Find the decimal value of 175 octal:

Convert (175)8 to (n)10

Octal Value 1 7 5
Power of 8 82 81 80

=> 1*82 + 7*81 + 5*80
=> 64 + 56 + 5
=> 125

So we have

(175)8 = (125)10