how to estimate table size

Hello friends,
I need to load data from a temporary table I created as a result of loading data from a text file to a real production table which I still need to create. This new production table won't grow, i.e. no inserts, no updates expected.
I am thinking about creating just one extent equal to the size of my temporary table. That case I'll use my storage efficiently.
How do I estimate the size of the extent I need? I already analyzed my temp table. Would it be avg_row_len*num_rows?
Any suggestions welcome.
Thank you.

average row length in bytes * num rows will give you an estimate of how many bytes the table is. you'll probablly want to create it with a bit more space for safety and possible unforseen updates but in general that will give you a good estimate.