It depends on how many DVDs you want to transfer to the USB and what settings you choose. If you simply need to make digital copies of your DVD collections to USB drives with exact same quality & data, you may convert DVD to ISO image, which will be as large as the DVD movie. Then you may need a USB stick with a larger capacity. If you convert DVD to MP4, a DVD can be shrinked to 1~2GBs. WinX DVD Ripper Platinum is able to reduce 80% of the original DVD size. That means, a 4.7GB DVD can be ripped to a movie at ~700MB. A 256GB flash drive at about $35 is can store 300+ DVD movies.