Heights

• The height of a king mattress depends on what king it is. Firm mattresses may be as short as 6 to 8 inches, while pillow-top mattresses may be as high as 17 inches. Memory foam mattresses are between 4 and 14 inches while latex mattresses can be anywhere from 10 to 15 inches.
  
  

Softness and Firmness

• The height of the mattress will greatly determine its softness/firmness. A shorter mattress will typically be much firmer than a taller mattress. The extra height on taller mattresses is usually to accommodate the extra padding atop the primary innerspring mattress. Memory foam king mattresses may be shorter than pillow top king mattresses, but they are usually the softest option available because of the foam material in their construction
  
  

Diminishing Height

• The height of your king mattress will inevitably diminish over time. As you sleep on it, the springs will weaken or the padding will be pushed down. Pillow top mattresses will lose their height faster than firm mattresses. This is because the softer top is easier to pad down than a firm top. You can circumvent this by purchasing a firmer, shorter mattress and a king-sized mattress pad that is easier to replace than an entire mattress.
  
  

Other Dimensions

• Eastern (standard) king mattresses are 76 inches wide and 80 inches long. California king mattresses are narrower, but longer. They are 72 inches wide and 84 inches long. California kings are better for taller people or narrower spaces.