There is no true standard window size, but most residential windows are around 24 to 30 inches wide and 48 to 56 inches tall. The size of the windows that are available for different areas of the home are dependent on the type of windows that are generally used in that area of other homes.
Bay windows, sliding windows and picture windows are generally available in sizes that are much larger than the commonly produced windows. These windows are meant to be larger sizes and will be available for homeowners who wish to have a large window to look out of. These windows do not follow any type of standard sizing and are generally available in custom sizes depending on the homeowners particular needs.
Basement windows are generally smaller than the windows that are most commonly produced for homes. Due to the different needs that homeowners have in their basements, the windows will be much smaller and will be able to provide the minimal light that is often needed in a basement. There is often less space in a basement for taller windows due to the foundation. Basement windows are generally between 18 and 24 inches wide; they are between 12 and 18 inches tall.