Split Head mattress Dimensions are usually either split head queen size which is 60 inches wide and 80 inches long, split head king size which is 76 inches wide x 80 inches long or split head California king which is 72 inches wide and 84 inches long. These are standard split head bed size bed measurements. Split head sheets are for split head adjustable beds where the mattress is split at the top only and the middle section of the mattress down to the foot is fixed. The actual split length can vary. Split head Size Mattress depths can vary from 6 inches to 14 inches or more, depending upon the manufacturer. Many times, actual mattress dimensions will vary by one or two inches, usually smaller.