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How do we say km2 in words? Do we use km exponent by two, square kilometer, kilometer squared or something else?

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Another "or something" pronunciation is 'hectohectares'. –  jwpat7 Oct 12 '11 at 18:03
    
but, please, the equivalent in imperial units, "square feet", is sq. ft., not ft² –  nohat Oct 12 '11 at 22:51
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up vote 25 down vote accepted

When talking about it as in a formula, you would say "kilometer squared". You would typically use "square kilometer" when discussing area, as in "his farm was three square kilometers".

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As I use the terms, "square kilometers" and "kilometers squared" are different units. 10 square kilometers is a square with an area equal to 10 times the area of a block 1 kilometer on each side. 10 kilometers squared is a block 10 kilometers on each side, thus 100 square kilometers in area. I parse them as 10 (square kilometers) and (10 kilometers) squared. –  David Schwartz Oct 12 '11 at 20:01
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@David: Wouldn't you normally just say 10 by 10 kilometers for the latter? –  Cerberus Oct 12 '11 at 20:21
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I believe that people say "kilometers squared" when reading off a formula or a value because this word order matches the order of the characters on the page, which means they don't need to "read ahead" to see the 2 before saying "kilometer" as they read the formula from left to right. I've never heard of "kilometers squared" meaning anything different from "square kilometers". –  Ryan Thompson Oct 12 '11 at 21:21
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@scottishwildcat: I agree. I did some googling and couldn't fine any evidence that anyone actually uses it. (And to Cerberus: Not if it wasn't 10 by 10 kilometers. It means of equivalent area to such a square. The idea is to avoid large and confusing numbers, primarily with non-metric units that don't have prefixes.) –  David Schwartz Oct 13 '11 at 10:49
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@David: I have always understood a block 10 kilometres on each side to be "10 kilometres square", not squared. Reading "km^2" as "kilometres squared" is not uncommon (though this perhaps doesn't make it right, and in careful speech I would say "square kilometres"). –  Billy Oct 13 '11 at 22:03
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Depends on the context.
If you are referring to an area then square kilometres is correct - but if it's a scientific unit that happens to be in length^2 then kilometres-squared.

edit: Checked the SI recommendations.

Although in general you would say kilomtres-squared when reading a formula, they recommend that if the length^2 represents an area eg. Pressure = N/m^2, then you read it as newtons-per-square-metre, since it is the area of a real square metre. I can't off-hand think of any units that are length^2 where it isn't an area.

However if the unit has a different quantity squared, such as Acceleration = m/s^2 then you read it as per-second-squared since a square second has no meaning on it's own.

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Square kilometers (or kilometres).

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The correct terms when written in a formal context are:

kilometres squared

or

square kilometres

Remember these are different.

Three kilometres squared is three kilometres on one side and three kilometres on the other side which is 9 square kilometres.

Three square kilometres is three kilometres on one side and one kilometre on the other side.

In a formulaic context 3 kilometres squared is written

3Km x 3Km

And 3 square kilometres is written like this

3Km2

with the two being an exponent (supertext).

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Three kilometers squared would be (3 [km])^2 which in turn will become (3 [km])^2 = 3 [km] * 3 [km] = 9 [km^2]. To make it less confusing you should treat units seperate from the values. –  Spoike Nov 3 '11 at 11:36
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Am I alone in saying "km²" as "kay-emm squared"?

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Lonely Izkata... –  GEdgar Oct 13 '11 at 0:08
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Would upvoting this answer mean agreeing ("Yes you are alone") or "No, I say that too"? :-) –  ShreevatsaR Oct 13 '11 at 1:53
    
@ShreevatsaR: I'm fine with either wink wink nudge nudge =^_^= –  Izkata Oct 13 '11 at 2:24
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