Most curtain panels are available in standard lengths of 63 inches, 84 inches, 95 inches, 108 inches and 120 inches. Pre-made curtains are generally 48 inches wide.
Floor-length curtains are usually most desirable unless a radiator or deep window sill prohibits this. When measuring curtains, using a metal tape measure is best because fabric tape measures can bend and provide an inaccurate measurement. It is best to start at the floor and measure up to the curtain rod. Rounding the measurement up is recommended because curtains can be hemmed easily if they are too long.
To ensure curtains are wide enough when closed, the combined width of all panels should be approximately 2.5 times the width of the window. If the homeowner doesn't intend to close the curtains, the curtain width may be decreased to 1.5 times the width of the window. When purchasing pleated curtain panels, it is best to choose a width equal to that of the window.
Choosing the location of the curtain rod depends on the style the homeowner desires. To achieve a traditional look, it is best to place the curtain rod 6 inches above the window frame and extend it 3 inches beyond the sides. For a more contemporary feel, the curtain rod may be placed anywhere from 6 inches above the window to ceiling height.