What is the meaning of キロ四方?

Question

Especially in the context of this sentence:

およそ二十キロ四方の巨大な湖は、ひっくり返した瓢簞のような形をしており、上の湖と下の湖に分かれている。

To my understanding, this sentence translates as "This lake was approximately twenty square kilometers in size, and resembled an inverted gourd, divided into an upper and lower lake." But I've seen a translation which said "This enormous lake had a radius of approximately twenty kilometers," which I don't particularly get. キロ四方 means 'square kilometer', right? Is "radius of 20 kilometers" a mistranslation?

Answer 1

I would say neither of the translations is correct. 20キロ四方 basically means "20 km × 20 km" (that is, 400 km²). 四方 literally means "four sides (of a square)". 平方キロ is the word for "square kilometer" (平方 = square, x²).

• 20キロ四方 = 20 km × 20 km
• 20平方キロ = 20 km² = 20 square kilometers

^{(Confusingly, we also say 20キロ平方, which literally means "20 kilometer's square" and thus is a synonym for 20キロ四方 = 20 km × 20 km.)}

For example, this article says 5キロ四方 referring to a 5 km square grid (i.e., each cell is 25 km² in area).

キロ四方 is usually used with square-like objects, but of course a real lake is not square. In a case like this, you can think it's roughly 20 km in diameter (not radius), or "20 km from north to south and 20 km from east to west".