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# A to Z of Excel Functions: The OCT2DEC Function

10 April 2023

Welcome back to our regular A to Z of Excel Functions blog.  Today we look at the OCT2DEC function.

The OCT2DEC function

This function converts an octal number (base eight) to a decimal number (base ten).

The OCT2DEC function employs the following syntax to operate:

OCT2DEC(number)

The OCT2DECfunction has the following arguments:

• number: this is required and represents the octal number you wish to convert.  It should be noted that number cannot contain more than 10 octal characters (30 bits) and that the most significant bit of number is the sign bit.  The remaining 29 bits are magnitude bits.  Negative numbers are represented using two's complement notation.

Two's complement is a mathematical operation on binary numbers, as well as a binary signed number representation based on this operation.  The two's complement of an N-bit number is defined as the complement with respect to 2N; in other words, it is the result of subtracting the number from 2N.  This is also equivalent to taking the ones' complement and then adding one, since the sum of a number and its ones' complement is all 1 bits.  The two's complement of a number behaves like the negative of the original number in most arithmetic, and positive and negative numbers can coexist in a natural way.

It should be further noted that:

• if number is not a valid octal number, OCT2DEC returns the #NUM! error.