A4 size is 210 x 297 mmA4 is the size of a standard letterhead
A5 size is 148 x 210 mmA5 is hald of A4
1/3rd A4 / DL size is 99 x 210 mm1/3rd A4 / DL is a third of A4
A6 size is 105 x 148 mmA6 is a quarter of A4