How to find the image size stored in table .. datalength did not work !

Hi,
I am at SQL 2005 . we have a table that stores pdf files along with file id. it is of data type of image. we are in the process of archieving the old images and we need to find the size of individual file size in the row and then sum up and come with total size that we can possibly save.
Select fileID , Datalength (Image_field) /1024 AS "SIZE_IN_KB" from table_name
FileID Uniqueidentifier
Image_Field image
does not report the right size . NOT EVEN CLOSE.
is there any work around... we are running out of san space....
thanks for your help.

you can work around and use sp_spaceused to get the size of table data
exclude the computed datalength of other fields from that size.

Hi ,
We don't want table size. let me explain a bit more , we are in the process of archiving based on createdate . the table also has fileid and data fields. we are trying to get how much space we save month by month based on year. so we know how much data we are archiving.

i used datareader in c# to get size of the blob of type varchar(max) and give me same result as datalength in T-SQL
to avoid truncation, try to run
Select fileID , Datalength (Image_field) /1024.0 AS "SIZE_IN_KB" from table_name
Select fileID , Datalength (Image_field) AS "SIZE_IN_Bytes" from table_name