My comment was a bit tongue in cheek re the exact fpm quoted.
Difficult o give exact power/rod clues but try 100 rpm will change rod by 100 fpm as a starting point.
I dislike concentrating on flying too much by numbers in a visual circuit when you need your eyes outside because unfortunately circuit discipline can be very poor at some airfields. However if you are learning on a PA28 here are some numbers to try , 2100 rpm downwind, turn base , 1500 rpm/ flaps 25, and it should settle about 75 kts with no trim change required, then on final, full flap should give you about 65kts again with negligible trim change so it helps reduce the workload.