This persistent myth has been making the rounds for decades. Often a corollary comes with it: people slept sitting up because of the short beds. The answer is complicated.
Early American beds were made individually; there was no standard size. Some beds, especially those for children or teens, were shorter than today’s. Some were longer. Some people may have slept propped up on pillows, just as they do today, but beds were not made shorter because of that.
Visitors to historic houses are often surprised if the tour guide takes a measuring tape to a “short” bed and they find it is as long or longer than today’s standard 75” double bed. In 1981 Colonial Williamsburg curators surveyed the antique beds in the exhibition buildings and found that all of them equaled or exceeded 6’3”, the standard double or single bed length today. Some are as long as 80”, the length of today’s king or queen size. Moral: measure your antique bed first, then you can tell whether it is shorter or longer than modern examples.
So why do we think the beds are shorter? Because they look shorter. The high bed posts, fabric hangings, canopy, and plouffy mattresses make beds appear shorter in comparison than they are. And these beds are often situated in rooms with very high ceilings and large dimensions, which makes the beds appear small in a big room.
As for the short people, heights varied in the eighteenth century as much as they do today. But overall, people in the colonial era were not dramatically shorter than today. When Colonial Williamsburg historian Harold Gill compared the average heights of white male soldiers during the Revolutionary War in the 1770s to those serving in the US Army in the 1950s, the difference was only about two-thirds of an inch. Other similar studies have shown similar results. The Museum of London had a recent exhibit (thank you, Francis Classe, for the info) trying to debunk this same claim. They said that on average, people in medieval times were only 2-3 centimeters shorter than people today. An article in a 2010 issue of the Economist supports this–there is a long article about medieval warfare based on excavations into a mass grave of soldiers killed during the War of the Roses and in the section subtitled “Who are you calling short?” the author says that medieval men averaged 1.71 meters tall, just 4 centimeters shorter than a modern Englishman.
Interestingly, the average height of colonial American males does seem to have been significantly greater—up to 2 inches—than the average height of European males of the same time (colonial period), a result ascribed to better nutrition and healthier living conditions (fewer crowded cities with killer epidemics and diseases) in the New World than in the Old.
More recent studies have shown that in the past half century, the average height of Americans has, indeed, increased. Comparing soldiers from the American Civil War, who averaged 5′ 7 1/4″, with today’s average for men, 5′ 10 1/2″, shows an increase of over three inches, most of which occurred in the last fifty years. Did beds become larger in the last half century? Well, no, bed lengths didn’t change, but their relative popularity has. Ever since the 1960s, queen-size and king-size beds, with their extra 5 inches in length, have become increasingly popular to the point that the queen is now the bed of choice for most couples. It is rare for a mattress store to sell a plain double bed, something that used to be the standard for married couples. This is due at least as much to the increased weight of Americans as it is to any increase in height.