My db_block_buffers is 30,000 and the db_block_size is 2048.

So I have 61440000 (30,000*2048) bytes reserved for blocks. (approx 58 Megabytes).

This makes up part of the SGA. You need to know how much physical ram your machine has before you make drastic changes to the SGA.

I think the SGA is made up primarily of the Buffer Cache ( discussed earlier in my case it was 58 meg), the shared_pool_size, the large_pool_size, the log_buffer. Totalling these gives the SGA, make sure there is enough room for this in ram and then some as there are a few more uses for the SGA that are minimal but must be accounted for.

I think my total SGA is about 100 Meg.