^That's what gina32 wants to clarify......
a.n.other person may have mis-described something, or gina might want to make sure her own description is accurate.
18 in. approx per side would give you something like 2.25 ft^2, so I think jth means 21 inch per side approx.
I think the only way to resolve this ambiguity is to ask the advertiser, if possible. I would probably assume that "three feet square" means 3ft * 3ft (ie, nine square feet), but it's always ambiguous.
How was it actually written Gina. 3 Square feet is usually an indication of area not size. 3ft² is an indication of area and the object could be 3ft long by 1ft wide, or 6ft long by 6ins wide for example. If it was written as being "a" 3ft square then that is what it should be. ie 3ftx3ft. which incidentally is 9ft².
3 sq ft as a square is around 1 foot 3 in as a square
and yes as the number get bigger the words matter
after Hiroshima the americans flattened even more, 20 sq miles of Tokyo which they had flattened previously.
20 mi sq ( 400 sqmiles) doesnt bear thinking about - and no they didnt