These tubes of whitening gel are extremely large and powerful. The gel works amazingly! I have used gels before purchased from my dentist, and they were not as good as these. You put your trays in for only 45min- 2 hours and you can see a noticable difference starting day 1. My teeth are naturally sensitve so I only put mine in for 30 min and it still worked better than the over-night gel from my dentist. The instructions say that you can apply the gel to whitening strips if you don't have trays. If you have never used whitening gel before your teeth might get extra white "stains" on them from the gel after just one use because it is so powerful. But these are temporary and go away in anywhere from 1-4 hours. *just thought some people might want to know, becuase it freaked me out when it happened to me! It took my other gels 1-2 weeks to build up these "stains", so that shows you how strong this gel is. Also, There is enough gel to last months!Great buy!