Curtain Calculator

How Does the Formula Work?

The curtain calculator determines exactly how much fabric you need to make curtains for any window. Enter your window width, desired curtain drop (length), fullness ratio, number of windows, fabric bolt width, and pattern repeat — the calculator computes the total fabric in meters and yards, number of fabric widths needed, cut drop including hem allowances and pattern waste, and total widths to cut. Buying too little fabric means mismatched dye lots when reordering; buying too much wastes money. This calculator eliminates guesswork and ensures you purchase the right amount the first time, whether you are a DIY sewer, a professional upholsterer, or ordering from a curtain maker.

Understanding Fullness

Fullness (also called gather ratio) determines how much fabric is used relative to the window width. A fullness of 1.5× means the total curtain fabric width is 1.5 times the window width — this gives a casual, relaxed look suitable for tab-top or eyelet curtains. A fullness of 2× (the most common standard) gives elegant, well-defined folds ideal for pencil pleat and pinch pleat headings. A fullness of 2.5× provides luxurious, deep folds for formal rooms and triple pinch pleats. A fullness of 3× is the maximum, used for sheer and voile curtains that need extra volume to look full because the fabric is transparent. The right fullness depends on the heading style, fabric weight, and room formality.

Measuring Your Windows

Accurate measurement is the foundation of good curtains. For the width, measure the curtain pole or track — not the window itself. The pole should extend 15 to 30 cm beyond each side of the window frame so curtains can be drawn back without blocking light. For the drop, measure from the pole or track to your desired length: sill length (just touching the windowsill), below-sill (15 cm below the sill for a more formal look), or floor length (1 cm above the floor for a clean line, or pooling 5 to 15 cm on the floor for a luxurious effect). Always measure at three points across the window — walls and floors are rarely perfectly level. Use the longest measurement to ensure full coverage.

Fabric Width and Pattern Repeat

Curtain fabric comes in standard bolt widths, most commonly 140 cm (54 inches) for drapery fabric and 280 to 300 cm (110 to 118 inches) for sheer fabric. Wide fabric (280 cm) can sometimes cover a standard window in a single width, dramatically reducing fabric needs and eliminating seams. Pattern repeat is the vertical distance before the design repeats — it can range from 0 cm (plain fabric) to 64 cm or more for large prints. Each cut length must be adjusted upward to the nearest complete pattern repeat so patterns match across fabric widths when sewn together. Large pattern repeats generate significant waste — a 64 cm repeat on a 260 cm cut drop wastes 60 cm per width. This calculator accounts for this waste automatically so you do not run short.

Heading Styles and Their Requirements

The heading (top) of the curtain determines both the look and the fullness required. Pencil pleat (the most common) uses 2 to 2.5× fullness with special heading tape that creates uniform narrow folds. Pinch pleat (also called French pleat) uses 2 to 2.5× fullness and creates groups of two or three pleats spaced apart — elegant and structured. Eyelet (grommet) curtains use 1.5 to 2× fullness with metal rings punched through the fabric — modern and casual. Tab-top curtains use 1.5× fullness with fabric loops — relaxed and informal. Wave (S-fold or ripplefold) heading uses 2× fullness and creates a continuous wave pattern — sleek and contemporary. Each heading requires different hardware (poles, tracks, gliders) so plan the heading before measuring.

Lining and Interlining

Lined curtains hang better, last longer, protect fabric from UV damage, improve insulation, and block more light. Standard cotton lining adds body and protects the face fabric. Blackout lining blocks virtually all light — essential for bedrooms. Thermal lining adds insulation value, reducing heating costs by up to 10 percent according to the Energy Saving Trust. Interlining (a soft flannel layer between face fabric and lining) adds luxurious weight and improves drape dramatically — it is standard in bespoke curtains. When ordering lined curtains, you need the same fabric quantity for lining as for face fabric. This calculator computes face fabric; simply double the result if you need matching lining yardage.

Cost-Saving Tips

Choose plain or small-pattern fabrics to minimize waste from pattern matching. Select 280 cm wide fabric for standard windows — fewer seams and less total fabric needed. Consider sill-length curtains instead of floor-length for less fabric consumption. Order all fabric at once from the same dye lot to avoid color variations between batches. Buy 10 percent extra as a safety margin for cutting errors and potential future repairs. Compare the cost of ready-made curtains versus fabric plus making-up charges — sometimes ready-made is more economical for standard window sizes. For multiple identical windows, calculate all together for the best cutting plan that minimizes waste.