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In America, a bed suitable for a single person (child) to sleep in is known as a 'twin bed', whereas in England it is a 'single bed'.

Any ideas on why it is called a twin bed in America?

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In the US, we do have a bed size called "super single" (which I had in college). It is longer than a twin though. – Kosmonaut May 30 '11 at 17:42
@Kosmonaut: I've never heard the term "super single". The mattress size popular in college dorms is "extra-long twin". – Marthaª May 30 '11 at 21:16
@Martha: Well, it is listed among the other sizes on Wikipedia. I never claimed my college's bed size was the most popular. It is just where I know the term from. – Kosmonaut May 30 '11 at 21:23
Twin size beds are the same size as a Single, but come in pairs, thus the reason for naming them Twin. – Frank R. Sep 25 '12 at 3:17
I always thought it was because we couldn't count. – Sven Yargs Mar 8 '13 at 4:33
up vote 1 down vote accepted

Twin bed is either of a pair of matching single beds ready to be joined to another twin bed to create twin beds. The word simply describes a bed which is stackable with another bed. A single bed isn't stackable, at least not the way you'd want it to.

UPDATE according to what John Y commented:

Well, wikipedia says:

U.S. terminology refers to a twin bed to mean what is known as a single bed in other countries, whereas other countries understand twin beds to be two single beds in the same room.

While wiktionary says:

twin bed (plural twin beds): Either of a pair of matching single beds.

Oxford dictionary says:

one of a pair of matching single beds, particularly in a hotel or guest room intended for two people.

So to sum it up, and now correct me if I'm wrong:

1 bed (US): twin bed
2 beds (US): twin beds

1 bed (UK): single bed or a twin bed if it belongs to a pair of beds
2 beds (UK): twin bed or twin beds

Therefore twin bed is ambiguous, unless the dictionaries are wrong.

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This answer might be helped by citations. I am having trouble visualizing the way the component single beds are supposed to be joined or stacked. (For one thing, "joining" to me implies horizontal abutment while "stacking" implies something vertical, like a bunk bed, or some kind of crazy Princess-and-the-Pea arrangement.) Finally, it's wrong to say "Americans don't call single beds twin beds", because they (we) very plainly do, correctly or not. – John Y May 30 '11 at 20:49
@John Y: Some twin bed frames have bedposts that are high enough that they can be stacked (see bunkbedscentral.com/main/…). They can also be joined side-by-side (with a thick enough mattress pad, and covered with double-bed sized sheets) to act as a double bed. – Jay Elston May 30 '11 at 23:39
@Jay Elston: Thanks for the information, though that serves to add a little more confusion regarding double beds, because there is a bed size called "double" which is clearly much smaller than twice a single or twin. (To the naked eye, two North American twin beds side by side look very much like a king.) See Kosmonaut's excellent Wikipedia link on bed sizes in the main comments to this question. – John Y Jun 2 '11 at 5:24
So then why does a "Double" size bed exist?.. Twin sounds ambiguous. – Frank R. Sep 25 '12 at 3:01

Small cot-sized beds are often found in pairs: in barracks, dormitories, prisons, hospitals, children's rooms, and other places. Perhaps such beds were frequently referred to as "twin beds" formally or informally at the time that bed sizes were being standardized, and furniture manufacturers just decided to keep the name that everyone had been using for that size of bed anyway.

So why are they called "twin beds" even when they don't appear in pairs? It may be something of a backformation: if two such beds are twin beds, obviously one such bed must be a twin bed.

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I have always supposed that it was a back formation from hotel parlance, but the examples of the phrase in the OED suggest that it is in reference to the sleeping arrangements of married couples: twin beds versus a double bed. – Colin Fine May 31 '11 at 14:50

Double or Full is larger than a twin (single) and smaller than a queen. Double means two people (double) can sleep on it if need be and the term FULL I think is because it is a full sized bed, not a kids single bed, or twin.... lol 2 twin beds side by side IS a King Sized bed. I think the term TWIN refers to the variations in which it can be used... it has a "twin" to make a King, a "twin" to make bunk beds, so if a child is part of a twin set..... Identical, etc., THAT person would refer to themselves as a twin.

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