Steel Interior Frame With Poly Jacquard TWIN XL DIMENSIONS – The dimensions of this XL twin size box spring are 78.7 x 38 x 9 inches. The length is 5 inches longer than our Standard Twin size. Please measure your bedframe to ensure compatibility. EASIER THAN EVER ASSEMBLY – As if its ultra-durable steel structure and convenient packaging weren’t impressive enough, this new box spring features tool-free locking brackets for intuitive setup, assembly takes only minutes to complete DURABLY ENGINEERED – Durable steel is used to construct the inside framework of this foundation; twin/twin xl sizes support a maximum weight capacity of 350 lbs, while Full, Queen & King sizes can support up to 700 lbs THOUGHTFULLY PACKAGED – All parts and instructions are packed into one compact box that ships straight to your door