Hang curtains at the right height.
A useful starting point is to mount a curtain rod about 4–6 inches above the window frame, then extend it roughly 3–6 inches past each side. Measure curtain length from the actual hanging point on the rod or rings down to your chosen hem position—not from the top of the window.
Start with the window and wall, not a package size
Measure the width of the window frame and the distance from its top to the ceiling. Note trim, a radiator, a deep sill, or furniture that may keep fabric from hanging freely. Decide whether the curtains need to block light, provide privacy, or simply frame the view. Those needs affect both rod width and fabric length.
In many rooms, a rod 4–6 inches above the frame looks balanced. If there is little space above the window, mount as high as the hardware can safely fit; if the ceiling is tall, you may choose a higher position. These are design starting points, not a construction standard.
Extend the rod beyond the window
Let the rod reach roughly 3–6 inches beyond the frame on each side when the wall allows it. This gives panels room to stack when open and keeps more glass visible. A 48-inch-wide window with 6 inches of extension on both sides calls for a rod span of about 60 inches, before accounting for finials or a maker’s bracket requirements.
Check that the rod will clear nearby corners, wall lights, and cabinet doors. If there is no side clearance, use the width you have and expect the open curtains to cover more glass. Follow the rod manufacturer’s span and bracket-placement instructions, particularly for heavy fabric.
Measure panel length from the real hanging point
Once the rod height is chosen, measure from where the fabric actually begins to hang: the underside of a rod for some headings, the bottom of a ring or clip for others, or the track carrier for a rail. Measure to the floor at several places because floors are not always level. Use the shortest drop if you want every panel to clear the floor.
For a tailored look, panels can hover around ½ inch above the floor. A fabric that just touches the floor needs more precise measuring. Puddled curtains require additional length and can be awkward where people walk or clean frequently. If a radiator or furniture sits below the window, a sill or apron length may work better.
Do one example before buying
Suppose the frame top is 84 inches above the floor and you place the rod 5 inches higher. The rod is now around 89 inches from the floor. If the fabric begins at that height and you want a ½-inch clearance, the target finished drop is about 88½ inches. The actual panel length may differ because rings, clips, a rod pocket, or hemming change where the fabric starts.
Check the finished length printed on the curtain, not just the package name. Wash or steam fabric according to its care instructions before making a final hem, since some fabrics change after cleaning.
Mark, check, then install
Use a level to mark both bracket positions and hold the rod in place before drilling. Make sure the window and door can open, and that the panels will not sit on a heat source. Install hardware appropriate to the wall and load; heavy curtains need more than a guess about anchors. If you rent, get approval before drilling and do not assume an adhesive alternative can hold a heavy rod.
A simple measuring sketch with window width, rod height, rod span, and desired finished drop prevents most ordering mistakes. Take that sketch to the store or keep it on your phone.