Average bed height varies between 16 to 26 inches from the floor to the top of the mattress, but some beds are higher or lower. You choice is determined by comfort, ease of access, decor style, and your need for underbed storage rather than bed size -- a twin-size bed can be the same height as a king, for example.
Easy and safe access, especially for elderly and infirm sleepers, requires that the person's feet touch the floor while the knees remain level with the hips when sitting on the edge of the bed. For most people, this requirement is met with a mattress height of 18 inches. Taller or shorter people require adjustments in bed height.
Tall beds, up to 36 inches, lend a formal look compatible with traditional decor styles. Four-poster beds often require tall mattress heights. Low beds, including futons, make the room look more spacious; they blend with contemporary and "zen" decor styles.