How to Measure Windows for Perfect Curtains

Before You Pick Up the Tape Measure

Getting curtains to hang beautifully starts long before you thread a needle. It starts with a tape measure, a pencil and a few quiet minutes at the window. Measuring is not difficult, but it is unforgiving: fabric cut too short cannot be stretched, and a pair that is too narrow will never look generous no matter how carefully you press the pleats. So let's take it slowly and get it right first time.

You will need a metal tape measure (a soft dressmaker's tape sags and gives false readings), a pencil, paper and ideally a helper for wide windows. If you are ordering a made-to-measure track or pole, fit it before you measure for fabric, since the track width and the height at which it sits determine everything else.

Have a think about the following before you begin:

• Track or pole? Poles need space either side for the finials and brackets.
• Where should the curtains finish? Sill, just below the sill, or full length to the floor?
• What heading will you use? Pencil pleat, eyelet, pinch pleat and wave all sit differently at the top.
• Are there radiators, window handles or sills in the way?

Measuring the Width Correctly

Here is the single most common mistake: measuring the window rather than the track or pole. Curtains should extend beyond the glass at both sides, typically by 15–20cm each side, so that when they are drawn they cover the frame and reduce draughts and light leakage. The width you need for fabric calculations is the full width of the track, or the distance between the two end brackets of the pole (ignore the finials themselves).

To that figure you then add the following allowances:

• Returns: if the track or pole is set away from the wall, the fabric must travel back to the wall at each end, usually 5–10cm per side. Measure this distance, do not guess it.
• Overlap: for a pair of curtains meeting in the centre, add roughly 5cm per curtain so they overlap and close properly rather than leaving a sliver of light.

Record the total as your finished track width. This is the number you will multiply for fullness in a moment.

Measuring the Drop

Drop is measured from the top of the curtain to the bottom. Where exactly you start depends on the heading. For a track with hooks, measure from the top of the track down. For a pole with rings, measure from the bottom of the ring, because the hooks sit below the pole. For eyelet curtains, the pole passes through the eyelets, so measure from the top of the pole and add about 3cm for the fabric that stands above it.

Then decide your finish:

• Sill length: finishes 1–2cm above the sill so the fabric does not sit on it.
• Below sill: usually 15cm below, a practical choice for kitchens and bedrooms.
• Floor length: 1–2cm above the floor for a clean, casual look, or just touching for something more formal.
• Puddle: 5–10cm of fabric resting on the floor, lovely in a period room but hard-wearing on carpets.

Always measure the drop in three places — left, centre and right — and use the shortest reading. Floors and ceilings are rarely perfectly level, and curtains that skim the floor on one side and trail on the other are a daily irritation.

Working Out How Much Fabric You Need

Curtains need to be gathered, so flat width alone is never enough. Multiply your finished track width by a fullness ratio suited to your heading:

• Pencil pleat: 2 to 2.5 times
• Eyelet: 1.8 to 2 times
• Pinch pleat: 2.2 to 2.5 times
• Wave: 2 to 2.2 times

A 150cm track with a 2.5 ratio needs 375cm of fabric across the pair, so roughly 190cm per curtain before seams. Add 10cm per curtain for side hems and 15–20cm to the drop for top and bottom turnings. If your fabric has a pattern repeat, add one full repeat per curtain length so the motifs line up across the pair — a detail that makes homemade curtains look properly professional.

A Final Check Before You Order

Write everything down clearly: track width, finished drop, heading type and required fabric quantity. Then read it back and sanity-check it against the window. Does the finished width cover the frame generously? Does the drop clear the radiator? If you are making curtains yourself, chalk the measurements onto the fabric and hold a panel up to the window before cutting. Five minutes of checking saves a great deal of unpicking, and your windows will thank you for years to come.