A5 is therefore double the size of an A6, measuring at 14.85 x 21 cm (roughly 6 x 8 inches) A4 is then double the size of an A5, measuring 21 x 29.7 cm (roughly 8 x 12 inches) A3 is then double the size of an A4, measuring 29.7 x 42 cm (roughly 12 x 16 inches)