6x12 U-Haul Cargo Trailer Dimensions: Inside dimensions: 12'3" x 6'4" x 5'5" (LxWxH) Door opening: 5'4" x 5'1" (WxH) How big is the 6x12 U-Haul Trailer? Well. It’s pretty big. You can fit an entire queen-sized bed inside with room for more. Just be sure that your vehicle can tow the gross vehicle weight. Find all listed towing vehicle requirements on our website. #UHaul #Trailer #Towing #MovingTips