In this image, the title on the left is issued in Folio (a hand-pressed sheet folded once), but the center and right are both issued in Quarto (a hand-pressed sheet folded twice). Of the latter two, the original folded-sheets of hand-press paper were different sizes resulting in one Quarto being much smaller than the other Quarto. Nevertheless, they are both considered Quarto.
folio-quarto
