The bed in its simplest form consists of soft padding held in a frame elevated above the floor. As might be expected, this concept was known at least as early as the Egyptian and Roman empires, and modern beds, the most commonly employed sleeping surface in the modern first world, descend from the dual-purpose sofas of that era. Common among the European upper classes through the intervening period, advancing standards of living finally brought the bed to the middle classes by the seventeenth century, and it has since become ubiquitous in modern western societies. In its modern incarnation, fully accessorized, a bed consists of the following components:

A bedstead, a frame typically made of sturdy wood or metal, or some combination thereof. The frame typically includes an (often ornamented) headboard at the head of the bed, a footboard at the foot (these directions referring to the orientation of a sleeper using the bed), sideboards connecting the two, securing and shielding from view the box springs and/or mattress and creating an overall rectangular frame, and some type of supports extending towards or across the center to bear the weight of the box springs, mattress, and any occupants of the bed. Modern frames typically elevate the occupants to around 3 feet off the floor for ease of getting into and out of the bed (leaving some space under the bed that is often used for storage or otherwise collects dust), but older beds were often raised higher to allow drafts to pass under the bed without chilling the sleeper. Likewise, some older beds incorporated posts mounted at the corners of the frame to mount a canopy and curtains for insulation (or, as with mosquito netting, to keep pests out). While the modern "airtight house" and heating technology has rendered these features obsolete, they may be found in vestigial form in newer beds for the sake of aesthetics.

Into this frame is placed a box spring, a pallet typically about 8 inches thick containing an arrangement of springs mounted to a solid base, or some other elastic mechanism. This absorbs weight from the occupants of the bed, and in so doing prolongs the life of a mattress, which would otherwise flatten from use earlier. Box springs are produced in a variety of tensions from very firm to fairly yielding, including adjustable models. Bunk, collapsible, or just plain cheap beds may replace the box spring with a set of springs integrated into the frame's supports.

On top of this goes a mattress, a pallet of roughly the same dimensions as a box spring, but softer and of different composition. The contents and structure of mattresses (and the resultant firmness) varies, but most modern mattresses rely on plastic foams or fabrics like cotton for cushioning, the latter often also incorporating "innerspring" coils, smaller than those found in box springs. Older mattresses often used down, feathers, horsehair, hay, or similar materials for padding. As the mattress serves as the sleeping surface, it is typically soft and comfortable, and can be used on its own. This softness, however, means less resilience, and mattresses should be flipped and rotated regularly to wear evenly and prevent sagging, especially for users who remain relatively still during sleep. Even with these precautions, mattresses may wear out and need to be replaced every decade or less.

Some modern mattresses replace some or all of the aforementioned filling with adjustable-pressure air chambers or, in the case of waterbeds, an encased pocket of water. These mattresses may take the place of both the traditional mattress and box spring, and provide additional comfort by conforming to the shape of a sleeper's body, but tend to be more expensive and may require specialized frames or controls.

Next comes a mattress pad, a thin pad placed (logically enough) on top of the mattress. Thicker mattress pads may add additional support and comfort to sleepers, but the pad's primary purpose is to provide a (washable) barrier between the mattress and the occupants of a bed, preventing irritation from any allergens in the mattress and in turn insulating the mattress from dirt, body oils, and germs introduced by sleepers. The mattress pad is typically secured to the mattress by means of elastic or tied straps at the corners.

A fitted sheet is then placed over the mattress and mattress pad, and is so named because it is fitted to the shape and size of the mattress, covering the top and sides of the mattress like a sleeve. Fitted sheets are generally held in shape by elastic at the corners, and are a relatively new development; earlier, flat sheets were laid over the bed and then folded under to achieve the same effect. Fitted sheets create a smooth, gentle sleeping surface, and come in a variety of colors, patterns, and styles. Bedclothes are usually bought as a set or otherwise selected to create a coherent "look".

One or more pillows are placed at the head of the bed, which the sleeper places his or her head on while lying down, providing support to the neck. Pillows, too, come in a variety of sizes, thicknesses, and contents, and are often wrapped in a pillowcase for the same ease-of-washing and stylistic concerns mentioned above.

One or more flat sheets, thin sheets of (usually woven) fabric, are then laid over the top of the mattress, perhaps tucked under at the foot of the bed. These are pulled over the body while in bed, where they serve as insulation, trapping warm air in a pocket around the sleeper. In warm climates or seasons, this may be sufficient to create comfort; if not, they supplement the insulatory effect of heavier bedclothes, and once again insulate these bulkier and more difficult-to-wash coverings from human dirt and grime.

Finally comes these coverlets, be they blankets, quilts, comforters, duvets or whatnot. Thicker and heavier (and thus better insulators) than sheets, one or more of these are usually pulled over the sheets during sleep, though they may be partly or wholly discarded (and recovered) during the night to moderate temperature. (These coverings and the flat sheets, when not in use, are either left as they were from their last use or pulled over the length of the bed and straightened, a process called "making" the bed which takes time but some find makes the bed look more attractive or feel more comfortable when they next use it.)

All these individual components must be made to fit each other, of course, and so for your consumption (and our mass production) convenience, beds are designed in a variety of standard sizes, again as listed below, with commentary:

  • Twin (Single) beds are 39 inches wide by 75 long, the first name coming from the fact that it is approximately half the size of a king bed; some may find using two twin mattresses and box springs easier than their larger, more awkward King-size counterparts. By themselves, they're best suited to children or as guest beds.
  • Twin Extra Long, at 39" wide by 80" long, is a relatively uncommon format most commonly found in college dorms or other institutional settings, where space is at a premium but beds must accomodate adult-height sleepers. It's difficult to find any bedsheets this size, let alone stylish ones, and when you move on, they won't fit anything else.
  • Double (Full) beds, at 54" wide by 75" long, fall far short of twice a single. While you can put two people in this bed, at 27 inches of space per person, it's not very comfortable, and if you plan to do this sort of thing regularly, you'd best look for something bigger.
  • Queen beds, at 60" wide by 80" long, can more feasibly fit two sleepers, but still leaves them with less individual space than they would have with individual singles. If you've not got that much space to work with, though, it's a decent compromise, and as a one-person bed, it's positively decadent.
  • King (Standard King, Eastern King) is the largest standard bed size, with 76 inches of width and 80 of length, and is common for two-person sleeping arrangements, and almost mandatory for more. If it'll fit where you want it, it's pretty much the way to go, though if you want a little more width or convenience, you might want to try two Twin or Twin Extra Long mattresses laid side-by-side.
  • California King (Western King), at 72" wide by 84" long, is the longest variant. If you really need 7 feet of length, the sacrifice of four inches of width is a decent tradeoff. As might be expected from the name, this size is more common, and easier to find bedclothes for, on America's West Coast.
Of course, custom sizes, or irregular and non-rectangular arrangements (heart-shaped, anyone?) are possible, but components and bedclothes usually must be specially ordered and produced at extra cost.