How much disk space do SQL Columns use

Does anybody know of a link where I can find this stuff out? I'm working on a proposal to drop a whole bunch of unused columns from a few tables, and if i could find out the amount of disk space used, that would really help me out.

For example, if i have a table with 5.5 million rows, how much space will i save if i drop a BIT/INT32/DECIMAL (18,2) column?

This is SQL Server 2008.

Thanks again!

Solution

There is big difference between column and real record allocation.

For types:

bit - is an integer that will be grouped to single physical column (saying 4byte integer) when you have more than one bit column in the record
int32 - takes 4 bytes
DECIMAL is very similar to structure described in http://msdn.microsoft.com/en-us/library/ms221061(v=VS.85).aspx (12-byte)

But in real world the columns are grouped to record with some alignment rules. Records are allocated by large pages, that can contains thousand records. The disk space is also affected by transaction journal - that partially saves some records. So it is difficult to deduce linear dependency of column size.