How are window dimensions generally determined in building plans?

Window dimensions in building plans are primarily determined by measuring the rough opening, which includes both the frame and the glass. This measurement is crucial for ensuring that the window fits properly within the wall structure and maintains the necessary insulation and weatherproofing standards. The rough opening size accounts for the structural elements surrounding the window, allowing for any installation allowances, such as shimming or adjusting during the actual window fitting.

While other factors like architectural design guidelines and the total area of the glass can influence the window's aesthetic and performance, they are secondary to the practical measurement of the rough opening. Additionally, the size of window treatments, such as curtains or blinds, is typically considered after the window is installed and does not directly determine the window dimensions specified in building plans.