The aspect ratio of of any item is the proportional relationship between its width and its height. It is commonly expressed as two numbers separated by a colon, as in 16:9. In case of windows it purely depends on the window sizes which are given by the architects/ designers/ specifiers. A Fabricator can always refer to the max & min size limitations given by AIS in the guidelines. It plays a major role in the structural stability & functioning of the windows. For e.g. in casement system the recommended aspect ratio is 1:1.5. Whereas in Sliding Height to Width Ratio should be less than 1:2.5