The silver ratio is, much like the more popular golden ratio a mathematical concept for proportions in geometrical figures.

The silver ratio of a rectangle is as follows: the ratio of the smaller side to the longer side equals the ratio of half the longer side to the smaller side.

     ___________
    |           | ↑ 
    |           |
    |           |
    |_ _ _ _ _ _| B
    |           |
    |           |
    |           |
    |___________| ↓ 

     ←    A    →


     A   0.5 B
     - = -----
     B     A


     A2 = 0.5 B2


     A     1
     - =  -- = 0.7071...
     B    √2

The silver ratio is found in ISO paper sizes. For instance, the dimensions of an A4 sheet of paper are 21.022 by 29.730 cm; a ratio of 0.7071.