Dammit! Someone wrote up the nodeshell before me. Ah well, I'll write my version, and they can fight it out.
Write your binary number down. Here's mine:

11010111

Now, divide it up into groups of

three, starting at the

right. If the

leftmost group has less than three letters in it, put

zeroes at the start to

make it up to three.

011 010 111

Now, this is similar to

Binary to Hexadecimal. For each group of three characters, write

numbers underneath. Start at the right, with 1, then

double it (2) and write that below the middle digit then double that (4) and write it below the leftmost digit. Example:

011 010 111
421 421 421

Now

multiply the top by the bottom for each digit, i.e.

011 010 111
421 421 421
021 020 421

Next, go along the

bottom line, adding together the groups of three numbers:

021 020 021
0 + 2 + 1 = 3
0 + 2 + 0 = 2
4 + 2 + 1 = 7
3 2 7

These are the

octal numbers for the little groups of three

binary digits. Now, if we squash them into one long number:

327

And there we have it; 11010111 Binary = 327 Octal

If you don't understand this, I'd check out my Binary to Hexadecimal node. It has better examples.