How can I measure for replacement windows?

Windows are measured from the jambs of the window. Measure the width and the head and sill of the window for the height. In many homes, the framework of the window is wood, while the jambs, head, and sill are the plastic-like material that holds the glass. Make sure your measurements are from the material holding the glass rather than including the frame around it. Any tape measure should provide a good measurement for your windows.