What is blueprint 620?

Usually, the paper of a3, a4, b5 and other specifications we use has a fixed size. 620 size paper is a kind of special size paper, which is often used in our life. For example, the wrapping paper we use has many specifications. There are five common specifications for drawing size, namely A0: 841mm×1189mm. A1:594mm× 841mm.a2: 420mm× 594mm.a3: 297mm× 420mm.a4: 210mm× 297mm. 。