I'm sorry -- I should've given directions specific to the two types of cast on methods (single and double) since that does make a difference in the number of knit rows.
The long-tail CO creates the first row of knitting since it is a double CO, and the first row after CO is done on the WS. So, for garter stitch:
[color=blue][i]Counting[/i] the cast on row as Row 1, that would be 48 rows total as ekgheiy said.[/color] The last purl ridge row is completed on the WS. So that means you have the CO (first row) + 47 rows garter st, beginning and ending on the WS.
With any single cast on method, the first row is on the RS and the cast on row is not counted. So the first purl ridge does not occur until Row 2. Again, the last purl ridge row, Row 48, is on the WS. So that means you have the CO + 48 rows, beginning on the RS.
I should've been clearer -- sorry! :oops:[size=2][/size][size=1][/size]