To accurately determine the needed length for your curtains, start measuring from the bottom of the curtain ring down to where you want the curtains to end. If you prefer floor-length curtains, measure down to the floor, leaving a gap of 1 to 2 centimeters to prevent the curtains from dragging on the ground. For window sill length, the measurement should end 1 to 2 centimeters below the sill. To ensure accuracy, it's advisable to measure at several different points around the window to account for any unevenness in the floor or slight differences in the installation points.