A curtain rod is the one fixing that decides how a whole window looks. Hang it right at the frame and the window looks small and the glass is half hidden by curtains even when they are open. Hang it higher and wider and the same window looks bigger, lets in more light and the curtains hang in longer, calmer lines. It costs nothing to move a rod on paper, so do that first.

Try it: place the rod and watch the window

Set your own window width and ceiling height, then move the rod. The picture shows the curtains pulled open to each side. Anything left over the glass is daylight you lose.

Window width (frame, outside)

Ceiling height

Rod past the frame, each side

Rod above the frame

Curtain stack when open (each side)

Rod length to buy

Glass still covered when open

Gap rod to ceiling

Window looks

Rod hard against the frameRule of thumbMake it look taller

Width: past the frame, not just across it

The main trick is to let the rod run past the window on both sides. When the curtains are open they bunch up beside the glass instead of in front of it. A common rule of thumb in guides is roughly 8 to 15 cm of rod beyond the frame on each side. A very narrow window can take more, and a bit more still looks generous, but keep it in proportion to the wall: a rod that runs into a corner or a wardrobe is a rod that is too long.

Now the practical part. Your rod length is the window width plus the overhang on both sides. Many rods are adjustable between a minimum and a maximum, so check that your number sits comfortably inside the range and not at the very end. Brackets go at the ends and, on wide windows, one in the middle, because a long rod with only two supports sags under heavy fabric.

Height: higher than the frame, below the ceiling

Common advice puts the rod about 10 to 15 cm above the window frame, or halfway between the top of the frame and the ceiling if you want the room to feel taller. Try the third button above: raising the rod makes the window read as tall because the eye follows the long vertical line of the fabric. Leave a few centimetres below the ceiling so you can still reach the rod and pass the curtain rings over the bracket.

Things that change the answer: a beam, a sloping ceiling, a radiator under the window or a shelf over it. In those rooms put the rod where it works and let the curtains stop where they stop. Use the rules as a starting point, then break them where the wall tells you to.

Measure before you buy

Four numbers are enough, and a tape measure and a pencil do the job.

• Frame width: measure across the outside edge of the window frame (trim included), not the glass.
• Free wall each side: how many centimetres of flat wall you have from the frame to the next corner, door or cupboard. This is your maximum overhang.
• Frame top to ceiling: this tells you how high the rod can go.
• What is behind the wall: check where you drill. Use a detector or avoid lines that run up from sockets and switches. If you rent, ask before drilling, or look at a tension rod or adhesive-hook option.

A heavy curtain pulls on its brackets all day. Use wall plugs that suit your wall (brick, plasterboard and so on) and screws long enough to hold, not just the ones in the box if they do not fit.

What to look for

At every budget, check the same things before you pay.

• Length range: your calculated length should sit inside the rod's adjustable range, not at the extreme.
• Diameter and weight: thicker tubes, often 25 to 28 mm, take heavier fabric with less sag. Thin rods suit light voile.
• Support: a centre bracket for anything over about 150 cm.
• Finish and end caps: pick a colour that matches the frame or the wall, so the rod disappears or becomes a quiet accent.

You may not need a new rod at all. If the old one is sound, simply moving the brackets higher and wider can change the look for free.