Window sizes range between 24 and 30 inches wide by 48 and 56 inches tall, according to Do It Yourself. However, this is just for single and double hung windows. Other styles can vary largely in their dimensions.
In the construction world, window sizes change a lot depending on their purpose and placement. Basement windows are smaller and wider than they are tall. Standard sizes range between 18 to 24 inches wide and 12 to 18 inches tall.
Other windows, like those made from glass blocks are limited only by the size of the block and the number of blocks used. A glass block is usually 5 3/4, 7 3/4 or 11 3/4 inches along the sides with various combinations of these measurements used for square and rectangular shapes.