Tools
Curtain calculator
Measure your window once and get the pole length, where to fix it, the finished drop and how wide your curtains should be for the heading you have chosen.
How the calculator sizes your curtains
Pole width
The pole or track extends past the window frame on both sides, usually by 15–25 cm (6–10 in), so that when the curtains are open they stack against the wall rather than blocking light. Wide windows and thick, lined curtains need more stacking space than narrow windows and sheers.
Pole height
A standard position is 10–15 cm (4–6 in) above the frame. Fixing the pole higher, close to the ceiling or cornice, makes windows and ceilings look taller and is a simple way to improve a low room. Check what is in the wall before drilling: there is often a lintel just above the window, which needs the right drill bit and fixings.
Drop
The drop is measured from the bottom of the rings (for a pole) or the top of the track down to where you want the curtain to finish. Floor-length curtains look best finishing about 1 cm (½ in) above the floor; puddled curtains add 5–10 cm (2–4 in); sill-length curtains finish just above the sill, and below-sill curtains about 15 cm (6 in) below it. If a radiator sits under the window, sill or below-sill curtains keep the heat in the room.
Fullness
Curtains need to be wider than the pole so they hang in folds when closed. Pencil pleats typically need about 2.5 times the pole length, pinch pleats about 2.2, wave headings about 2, eyelets 1.5–2 and tab tops about 1.5–1.75. Less fullness looks flat and skimpy; more looks luxurious but stacks more bulkily.
For heading styles, linings and fabrics, read our guide to choosing and hanging curtains.