Square Acres

Square acres sounds double to me. ODE does not list square acres as a word but does list square miles etc. The only "three-dimensional" word if you like that I found in the dictionary is acre-foot, which is the volume that fits into an acre (an area) times height of one foot.

Theoretically an area of land that is roughly rectangular or square shaped which encompanses 43,560 square feet might be loosely referred to as an "acre square".
This might have been used to demarkate house,building plots or farmland in some ex British colonies in the past.

It looks to me that the Google hits & definitions are people using "square acre" as a synonym for just plain "acre," or for an acre that is square in shape as opposed to a rectangle or something hopelessly irregular.

I think a lot of people visualize an acre as a square, based on the land surveys that were done in most of the US, which imposed a somewhat artificial grid system on the land, based on acres that were square. See diagram. A section is a square that is one mile on each side. It comprises 640 square acres.

An acre in its original definition is not a square but describes "the amount of land that could be plowed in one day with a yoke of oxen and measured by one chain in width (22 yards), and one furlong, or 10 chains in length (220 yards), yielding 4840 square yards" (source: Wikipedia).

A bit off topic, but when I was a kid, people sometimes still referred to the to the grass verges at the roadside as "the long acre". Before (much) motorised traffic, a smallholder would turn a cow out to graze on the road verges. An acre of this would be very long & narrow- very much the opposite of a "square acre".

But in the OP, the term "square acre" seems to be used in error. Maybe the writer is used to "square metre" or "square yard" & doesn't realise that "acre" is already an area.

I found the original review. It's a user review on Amazon

The book is The Song of the Quarkbeast. It's a fantasy novel, part of a series aimed at teenage readers. There is only one mention of "square acres."
>The castle covered an area of six square acres, with many of the Kingdom's administrative departments scattered among its two hundred or so rooms.

I did some searching and found many other uses of acre or acres in the author's novels. None of them are square. So, I'd say it's a hiccup, unless the fantasy kingdom has an alternate scheme of measurement.

An acre is already a 'square' unit, placing square here is just a poor example of English or a simple case of tautology. The review itself sounds a bit strange, perhaps he hit the booze a bit early that day !!