I think you will not get good estimates as it depends from many things like compression, number of vproc, number of rows, the actual plan etc.
explain gives you estimates on the estimated rows of each spool file. If estimates are good these might give you a best proxi.
If you can figure out which cols are affected in each spool you can sum up the byte lengths and multipy the number of estimated rows. Checking the lifetime of the different spool files might give you an upper limit.
But as mentioned above - a rather difficult business...
Thanks for the reply,
One more thing like from table DBQLogTbl we can get how much spool was taken by query, Is there any table where spool per amp is stored which was taken by query