Chose the format you want
A0  A1  A2  A3  A4  A5  A6  A7  A8  A9  A10  
B0  B1  B2  B3  B4  B5  B6  B7  B8  B9  B10  
C0  C1  C2  C3  C4  C5  C6  C7  C8  C9  C10 
DL  letter  legal 
Paper formats
A series of paper sizes is defined by ISO 2016.
The height divided by the width of all formats
of A, B and C series is the square root of two (1.4142)
Most popular:  A4  A0  DL  B1 
Interesting facts
 Format A0 has an area of one square meter.

Format A1 is A0 cut into two equal pieces.
In other words, the height of A1 is the width of A0.  Dimensions of B formats are geometric mean of two intermediate A dimensions. Dimensions of B2 sides are geometric mean of A2 and A1 sides.
 Dimensions of C format are geometric mean of appropriate A and B dimensions, i.e. C2 format is geometric mean of A2 and B2.
Series of C formats is mainly intended for envelopes.
Their numbering indicates what type of paper of A format can be put in a given envelope without folding, for example, A4 paper fits the C4 envelope without folding.