What is the normal Follicle size?

i have a 28 cycle..my doc said i have one mature follicle on left ovary and two on right measuring 2.4 cm (approx24mm). I wanted to kno what is the normal size for a follicle to conceive. my doc said all looks normal and have a pretty gud chance to conceive. sice i have one on left and tw on right.wht are my chances of conceiving twins with 3 mature follciles? was on clomid 5o mg.then 100mg then back to 50mg. this being my third cycle.