U-Haul King Mattress Bag - 96&rdquo; x 78&rdquo; x 10&rdquo; - 2 Mil Bag dimensions: 96 x 78 x 10 (L x W x H) Open at the 78 end for an easy slip on or off Also available in twin, full and queen sizes Two separate bags will be necessary if you are moving or storing a mattress and a box spring. If your king box spring is made of two twins, purchase one king size mattress bag and two twin size mattress bags