7.1 Beta 1 & table size calculation

I am looking at 7.1 beta 1 to see how my application (currently on 7.0.3) will operate under 7.1.   To calculate
usedspace, in 7.0.3, I lookup the relpages count for the table in pg_class and multiply it by 8 (8k is my block size).
Inmy testing of 7.1 beta 1, I created a record of length 24947, but the relpages count is only 1 (after a vacuum
analyze,and with block size of 8k).  Is the relpages counts under 7.1 no longer valid of the physical page storage???
andwhat would the correct way be to calculate this under 7.1 beta 1 ???? 

Thanks in Advance,
Dale.