Minimum measurement for a "mature" follicle

I am having an ultrasound tomorrow and I cannot remember what measurements for a follicle are considered to be good, healthy and mature?  Anyone know what it is?

[Heather5]

I think 18 mm and above is considered mature :-)

[sarah9010]

my doctor says anything 15 and over are considered to be mature eggs but they also wait till 18 for trigger or ovulation. i asked because i was wondering if any other smaller follies may have eggs in them and they said that at 15 they consider them to be mature and have a eggie...