noun
A6 paper size (105mm × 148mm)
Refers specifically to the ISO 216 A6 paper size, commonly used for pocket notebooks, postcards, and small booklets.
この手帳はＡ６判で、持ち運びに便利だ。
This notebook is A6 size, making it convenient to carry around.
A5 is the next larger size (148mm × 210mm), often used for notebooks and booklets.
B6 is a slightly larger Japanese standard size (128mm × 182mm), common for paperbacks.
From the ISO 216 A-series paper size designation 'A6' combined with 判 (はん, 'size' or 'format').