Curtain Calculator
Determine the right curtain dimensions, panel count, and fabric yardage for your windows. Choose your preferred length style and fullness factor to get an accurate materials estimate.
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Measuring Your Windows Correctly
Accurate measurements are the foundation of good-looking curtains. Measure the window width from the outside edge of the frame on each side. Add 3 inches per side for rod overhang so curtains can stack off the glass when open.
For height, measure from where the rod will sit to the desired endpoint: sill, below sill, or floor. Most designers recommend mounting the rod 4 to 6 inches above the frame to create the illusion of taller windows. Measure from the intended rod position, not the top of the frame.
Measure each window individually even if they look identical. Older homes can have windows that vary by an inch or more. Use a steel tape measure and measure twice before calculating fabric needs.
Choosing Curtain Length Styles
Sill-length curtains end at the window sill, giving a clean look suited for kitchens and bathrooms where longer curtains would be impractical. Below-sill curtains extend 4 inches past, adding a more finished appearance while avoiding interference with radiators or furniture.
Floor-length is the most popular option. The curtain hangs to half an inch above the floor, creating an elegant look that works in living rooms, bedrooms, and dining rooms. This length makes rooms feel taller, especially with the rod mounted near the ceiling.
Puddle curtains pool 2 to 6 inches of fabric on the floor for a luxurious effect. This style works best in formal rooms with minimal foot traffic, as the pooled fabric collects dust. Silk and velvet drape particularly well in this style.
Fabric Selection and Yardage Tips
Fabric weight determines how curtains hang. Sheer fabrics like voile filter light with minimal privacy. Medium-weight cotton and linen blends balance light control and privacy. Heavy fabrics like velvet and blackout materials provide maximum light blocking and insulation.
Always buy 10 to 15 percent more fabric than the calculator indicates. The extra covers pattern matching, hemming, heading allowances, and cutting waste. Standard headings require 4 to 8 extra inches at the top depending on style: rod pocket, grommet, or pinch pleat.
When sewing from decorator fabric, the bolt width (typically 54 inches) differs from the finished panel width after seams. Plan for 2 inches of side-hem allowance per panel and 4 inches for the bottom hem. These additions increase total yardage beyond the basic dimensions.
Frequently Asked Questions
What is a fullness factor for curtains?
The fullness factor determines how gathered or pleated your curtains look when closed. A factor of 2 means the total fabric width is twice the rod width, creating a standard gathered appearance. A factor of 2.5 to 3 gives a luxurious, heavily gathered look common with pinch-pleat styles. A factor of 1.5 creates a more relaxed, flat appearance suitable for tab-top or grommet curtains.
How wide should a curtain rod be compared to the window?
The curtain rod should extend 3 to 6 inches beyond each side of the window frame. This allows curtains to stack off the glass when open, maximizing natural light. For a 48-inch window, a 54 to 60-inch rod is standard. Going wider, up to 12 inches per side, makes the window appear larger and allows curtains to clear the glass completely.
What is the standard curtain panel width?
Most ready-made curtain panels are 54 inches wide, which is based on the standard bolt width of decorator fabric. For windows wider than about 27 inches (half of 54), you need at least two panels to achieve adequate fullness. Custom curtains can be any width since fabric widths are seamed together during fabrication.
How long should floor-length curtains be?
Floor-length curtains should end about half an inch above the floor to avoid dragging and collecting dust. The standard measurement is from the rod to the floor minus 0.5 inches. If you prefer a slight break where the curtain just touches and folds on the floor, add 1 inch. For a dramatic puddle effect, add 2 to 6 inches beyond floor length.
How much extra fabric should I buy for pattern matching?
If your fabric has a repeating pattern, add one pattern repeat per panel to account for matching. Measure the vertical repeat distance and multiply by the number of panels minus one. Typical pattern repeats range from 12 to 27 inches. For a 24-inch repeat with 4 panels, add 72 extra inches (2 yards) of fabric to your total.