Smart driver I took a Gallon of Sand and emptied into a 8'' x 11'' x 2 5/8'' box and got 231 cubic inches, so the Formula is correct. Sand fills a C.I. better than growing Soil. Here's something else I did, I measured one of my 25 Gal. Container top to bottom was 18'' high,divided it by 2 and measured it at mid. point 9'' high, I then measured across it was 20 1/2'', I divided by two = 10 1/4'' inches, here's the equation ------->>

10.125'' x 10.125'' x 3.14(pie) x 18'' =5794.18 divided by 231= 25.08 Gallons, that would be filling my 25 Gal Container to the top.

Jeff I agree, a 42''x42''x 36'' =63504'' divided by (1 Cubic Ft.1728'') = 36.75 C.FT. Divided by 1 Cubic Yard (27C.Ft.)=1.36 Yards of Soil.

The first pic. appears to be around 4ft wide, maybe that one will hold that much, but the Pic. of the planters don't look big enough to hold 1.36 Yards of Soil, but according to measurements they will hold that amount, if those where inside dimensions.

Carlos