Curtain Width (Fullness) Calculator
Curtains look flat and skimpy when they are cut to the exact width of the window, because finished curtains need extra fabric to gather into folds. The amount of extra fabric is set by the fullness ratio, a multiplier applied to the area the curtains must cover. This curtain width calculator takes the width of the window or track you want to cover, the fullness ratio you prefer, and the number of fabric panels, then returns the total flat fabric width required and the width of each panel before hems. A light, casual look uses a fullness around two times, a standard pleated look uses about two and a half times, and a luxurious, densely gathered look uses three times or more. Choosing the right fullness is the single biggest factor in how the finished curtains hang. Every figure here is computed deterministically from your inputs, so the same window and fullness always return the same fabric width. Enter your measurements below to plan a fabric order, compare looks at different fullness ratios, or split the total evenly across panels, with a worked example that reconciles exactly to the calculator defaults so you can check each step before cutting or buying.
Total fabric width equals window width multiplied by the fullness ratio, then divided across panels. A 72 in window at 2.5 fullness needs 180.00 in of flat fabric, or 90.00 in per panel across 2 panels.
Curtain width formula
total flat fabric width = window width x fullness ratio
width per panel = total flat fabric width / number of panels
fullness ratio = 2 (light) to 3 (full), window width measured in inches
The fullness ratio multiplies the covered width so the fabric has enough material to fold and gather. Dividing the total across panels gives the flat width each panel must be cut, before adding side hems.
Worked example
Take a window 72 inches wide, dressed at a standard 2.5 fullness ratio with 2 panels.
- Total flat fabric width: 72 x 2.5 = 180.00 in
- Width per panel: 180.00 / 2 = 90.00 in
You need 180.00 inches of flat fabric in total, or 90.00 inches per panel, matching the calculator's default inputs exactly.
Curtain Width (Fullness) Calculator: frequently asked questions
What fullness ratio should I choose?
A fullness of about 2 gives a relaxed, lightly gathered look, around 2.5 is the common standard for pleated curtains, and 3 or more gives a rich, densely folded finish. Heavier or sheer fabrics may need adjusting, so this calculator leaves fullness as an editable input.
Does this include hems and seams?
No. The result is the flat fabric width needed to achieve your chosen fullness across the window. Add side hems (commonly one to two inches per side per panel) and any seam allowances on top of the per-panel width before cutting.
Why divide by the number of panels?
Curtains are usually made from two or more panels that meet in the middle or stack at the sides. Dividing the total flat width evenly across panels tells you how wide each panel must be cut so they share the gathering equally.
Should I measure the window or the track?
Measure whatever the curtains will actually cover. For curtains hung on a track or pole that extends beyond the window, measure the full track or pole length, not just the glass, so the curtains can close completely and overlap at the sides.
Can I use this for one wide panel?
Yes. Set the number of panels to 1 and the calculator returns the full flat fabric width as a single panel. Very wide single panels usually require joining fabric widths with seams, so plan for that in your fabric order.
Official sources
- Measurement, units and dimensional standards: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.