Curtain Size Calculator

How to measure for curtains

1. Measure the window width inside the frame (or the outside of the trim), then decide how far the rod should extend each side – commonly 4–10 in (10–25 cm) – so the open curtains stack beside the glass rather than over it.
2. Decide the rod height. Many decorators mount it about 4–6 in (10–15 cm) above the frame, or higher – even halfway to the ceiling or just below it – to make the window look taller.
3. Measure the drop from where the curtain will hang (the rod, or the top of the rings or hooks) to the sill or floor. Measure in three places, because floors and ceilings are rarely level, and use the shortest for floor-length curtains.
4. Use a steel tape measure; fabric tapes stretch.

How wide should curtains be?

Curtains need extra width so they hang in folds when closed. The multiplier is called fullness, and it depends on the heading style:

Example: a 48 in window with a 64 in rod (8 in each side) at 2× fullness needs 128 in of curtain width – two panels of about 64 in each. Ready-made panel widths are measured flat, so for this window you would buy two panels around 60–65 in wide, or more panels of a narrower width.

How long should curtains be?

For rings and clips, measure from the bottom of the ring, not the rod. For grommets, the curtain top sits slightly above the rod – check the manufacturer's guidance.

Standard ready-made curtain lengths

Sizes vary by brand and country, so check the exact finished length on the label. If you fall between sizes, buy the next length up and hem it, or adjust the rod height.

Calculating fabric for made-to-measure curtains

1. Total curtain width = rod length × fullness (add about 4 in per panel for side hems and overlaps).
2. Number of fabric widths = total width ÷ fabric width, rounded up.
3. Cut length = finished drop + heading allowance + bottom hem (often 6–8 in heading and 6–8 in double hem, depending on heading type).
4. If the fabric has a pattern repeat, round each cut length up to a whole number of repeats.
5. Total fabric = number of widths × cut length; divide by 36 for yards or 100 for metres. Lining is calculated the same way.

Example: 128 in of finished width on 54 in fabric needs 3 widths (162 in). With an 84 in drop and 16 in of hems, each cut is 100 in, so the total is 300 in – about 8⅓ yards. With a 27 in pattern repeat, each cut rounds up to 108 in, so you need 324 in – 9 yards.

Other things to consider

• Stack-back: open curtains take up space at each side (often roughly a quarter to a third of the curtain width); extend the rod further if you want the whole window clear.
• Blackout and thermal linings add weight and stiffness, so use a sturdy rod and allow a little extra fullness for smooth folds.
• Radiators and heaters: sill-length or below-sill curtains are safer than floor length directly over a heater.
• Bay windows: measure each section separately and use a bendable track or separate rods.

Full worked example

1. Window: 60 in wide inside the trim, top of the frame 82 in from the floor.
2. Rod: extend 10 in each side so the curtains stack clear of the glass – an 80 in rod – mounted 6 in above the frame at 88 in.
3. Width: pinch pleat at 2.25× fullness → 80 × 2.25 = 180 in in total, or two panels of 90 in.
4. Length: floor-length 'float', measured from the bottom of the rings at 87 in → finished drop 86½ in.
5. Ready-made option: two 96 in panels hemmed to 86½ in, choosing panels about 90 in wide (or three narrower panels per side).
6. Made-to-measure on 54 in fabric: 180 in ÷ 54 = 3.33 → 4 widths; cut length 86½ + 16 = 102½ in; total 410 in ≈ 11.4 yd – buy 11½ yd, plus the same amount of lining.

Layering, doors and special windows

• Sheers plus curtains: use a double rod or track; the sheer usually hangs at 2.5–3× fullness behind curtains at 2–2.5×, and the sheer is often made ½–1 in shorter so it does not show beneath the main curtain.
• French or sliding doors: mount the rod high and wide enough that open curtains clear the door completely and do not catch on handles.
• Café curtains: hang from a rod halfway up the window; width at about 1.5–2× and length to the sill.
• Arched or very tall windows: consider mounting the rod just below the ceiling, or use a custom track that follows the shape.

Rod or track?

Decorative rods suit grommet, tab-top and ring-hung curtains and are easy to fit. Tracks – mounted to the ceiling or wall – suit pleated and wave headings, allow smoother operation and can bend around bay windows. For heavy blackout or interlined curtains, check the rod's or track's weight rating and use a centre support on spans over about 5–6 ft.

Metric example

A 150 cm window with a 200 cm pole (25 cm each side) at 2× fullness needs 400 cm of curtain width – a pair of 200 cm panels. With the pole 230 cm above the floor and curtains floating 1 cm above it, the finished drop is about 229 cm. Made to measure from 140 cm fabric, that is 3 widths; with 30 cm of hems and heading, each cut is 259 cm, so you need about 7.8 m – buy 8 m.