How to work out curtain sizes
Curtains are the one soft furnishing where guessing is expensive: fabric is sold by the metre and a mistake means either a stingy, flat-looking window or a bill you did not need. Two measurements and one multiplier settle it. Measure the rod (not the window), decide the drop, then multiply by fullness — the amount of fabric gathered into each centimetre of rod.
1. Measure the rod, not the window
A curtain rod normally extends 10–15 cm (4–6 in) past the window frame on each side, so the curtains can be pulled clear of the glass and the window looks wider when they are open. The fabric has to cover the full rod width, so a 150 cm window on a rod extended 15 cm each side needs fabric for a 180 cm opening. Hanging the rod 10–15 cm above the frame — or all the way to the ceiling — also makes the room look taller, and it changes the drop.
2. Choose the drop
- To the sill: the classic neat finish; the curtain ends level with the window sill.
- Just below the sill: 10–15 cm past the sill, which stops draughts and looks more generous.
- To the floor: the most common modern look; measure from the rod to the floor and cut 1–2 cm long to allow for uneven floors.
- Puddle: 2–5 cm of fabric resting on the floor for a formal, hotel-style finish.
3. Multiply by fullness
Fullness is how much flat fabric goes into the gathered curtain: 1.5× for sheers, voile and light fabrics, 2× as the standard for most curtains, and 2.5× for deep, luxurious folds on pinch-pleat headings. The gathered curtain ends up the width of the rod; the fabric you buy is flat, so a 180 cm rod at 2× needs 360 cm of fabric.
Common window widths in both units
| Window width | Rod width (+15 cm / 6 in each side) | 1.5× | 2× | 2.5× |
|---|---|---|---|---|
| 60 cm / 24 in | 90 cm / 36 in | 135 cm / 54 in | 180 cm / 72 in | 225 cm / 90 in |
| 90 cm / 35 in | 120 cm / 47 in | 180 cm / 70 in | 240 cm / 94 in | 300 cm / 118 in |
| 120 cm / 47 in | 150 cm / 59 in | 225 cm / 88 in | 300 cm / 118 in | 375 cm / 148 in |
| 150 cm / 59 in | 180 cm / 71 in | 270 cm / 106 in | 360 cm / 142 in | 450 cm / 178 in |
| 180 cm / 71 in | 210 cm / 83 in | 315 cm / 124 in | 420 cm / 166 in | 525 cm / 208 in |
| 240 cm / 94 in | 270 cm / 106 in | 405 cm / 159 in | 540 cm / 212 in | 675 cm / 265 in |
The rod width column adds 15 cm (6 in) on each side of the window; multiply that figure by the fullness you want.
4. Allow for the heading and the hem
The fabric you cut is longer than the finished drop, because it has to fold over at the top and be hemmed at the bottom. Eyelet curtains need about 4 cm above the tape, pinch pleat and rod-pocket headings 10 cm, pencil pleat and tab top 8 cm, and the bottom hem is usually 10 cm (4 in) for a weighted, straight-hanging edge. Add both to the drop before you cut.
Eyelet or pinch pleat?
Eyelet (grommet) curtains are threaded straight onto the rod: they slide easily, need less fabric (1.5–2×) and suit modern rooms, but they hang in soft, relaxed waves and the rings are visible. Pinch pleat curtains use heading tape and hooks, need 2–2.5× fabric, and hang in crisp, even folds that suit traditional rooms — and because the pleats are fixed, the curtain keeps its shape when open. Whichever you choose, buy the fabric in one go: dye lots vary, and curtains are the one place where a shade difference is impossible to hide.
How many panels?
Split the total fabric width into two panels for a normal window — each panel covers half the rod and they meet in the middle — or into three or four for a very wide opening, where each panel gets too heavy to slide. Ready-made panels are sold by flat width (55 in / 140 cm is the most common), so divide the total fabric width by the panel width and round up to know how many to buy. If your per-panel figure is wider than the bolt, plan a join or choose a wider fabric — a 280 cm bolt cuts into two 140 cm panels with no seam at all.
Frequently asked questions
How much fabric do I need for a 150 cm window at 2× fullness?
With the curtain on the window frame itself, 150 × 2 = 300 cm (118 in) of flat fabric. In practice a rod usually extends 15 cm past the frame on each side, which makes the opening 180 cm and the fabric 360 cm (142 in) — the extra 60 cm is what stops the curtains from covering the glass when they are open.
What fullness should I choose for curtains?
1.5× for sheers, voile and light fabrics that are meant to look flat, 2× as the everyday standard for most curtains, and 2.5× for deep, luxurious folds on a pinch-pleat or wave heading. Heavier fabrics look fuller at a lower multiple; thin fabrics need more to avoid looking like a sheet.
Eyelet or pinch pleat — which is better?
Eyelet (grommet) curtains thread straight onto the rod, slide easily, need only 1.5–2× fabric and suit modern rooms, but hang in soft waves. Pinch pleat curtains use tape and hooks, need 2–2.5× fabric and hang in crisp fixed folds that suit traditional rooms. Pinch pleat costs more fabric and more to make; eyelet is the simpler, cheaper option.
How high should a curtain rod be hung?
Ten to fifteen centimetres (4–6 in) above the window frame is the usual answer, or all the way to the ceiling to make the room feel taller. Extending the rod 10–15 cm past the frame on each side is just as important: it lets the curtains clear the glass, which makes the window look wider when they are open.
How long should curtains be?
Sill length ends level with the sill, below-sill length hangs 10–15 cm past it, floor length just touches the floor, and a puddle leaves 2–5 cm resting on the floor. Floor length is the most popular today. Always measure from the rod, not from the window, and cut floor-length curtains 1–2 cm long so you can adjust them on the rod.
How many ready-made panels do I need?
Divide the total fabric width by the flat width of one panel and round up. A 180 cm opening at 2× needs 360 cm of fabric; with standard 55 in (140 cm) panels that is three panels, or two if you use a 280 cm bolt cut in half. Ready-made curtains also vary in how much fabric they contain, so check the flat width, not just the "suitable for window" label.