1.As shown in the illustration, measure the window opening at three different locations for width, height, and depth. If the three measurements are not the same, take the shortest measurement.
2.Carefully measure the distances between studs and the size of masonry openings. Your dealer will deduct an inch from the outer dimensions (height and width) when your order is taken.
3.Place a level on the window threshold and check whether it's level.
4.Use a square to see if all the corners are all perfectly square.