It states on my Listerine bottle to rinse 20mL for 30 seconds. I fill 80% of it in the cap. Is that enough? Or should I fill the whole cap, or a seperate cup? 2 answers by real people - How much is 20mL for Listerine? GetTopUp Team 1 month ago *shrugs* Do you really need to measure…? I usually just rinse with half or a little less than half a cap, and I am cavity and dental problems-free. Just do whatever works for you. If you feel the burn, then you’re good. 1 R.M. 61 1 month ago one capful is enough! 0 Share: