Window sizes of envelopes and pockets

DIN size window size position
DIN C6 
DIN Lang 
Oversized
45 x 90 mm 20 mm from the left, 
15 mm from the bottom
DIN C5 
DIN B5
45 x 90 mm 20 mm from the left, 
60 mm from the bottom, 
with flap on the right
DIN C4 90 x 55 mm 57 mm from the left, 
20 mm from the bottom, 
with flap on the left