We have a king bed, bought the King size and its about 6 too long in length and 4 on the width.  Really disappointed, sent the kiddo to the grandparents for the night so we could put this together without distractions and got it together and its too big. The thought of breaking it all down and packaging it back up is painful. But we cannot keep as our children could get very hurt with their legs getting stuck in the gaps. Did not think I would need to take measurements as I imagined all king sizes are universal and you shouldnt need a particular mattress or box spring. Be sure to measure your bed before purchasing and save yourself the hassle.