To calculate curtain fabric yardage, the window width, finished curtain length, pleat ratio, and fabric pattern repeat are required. The pleat ratio determines the extra width needed to cover the window opening. The pattern repeat adds vertical allowance so the design matches across panels. This guide provides the math for both plain and patterned fabric.
Step 1: Measure the Window and Decide the Finished Curtain Dimensions
The width of the window opening at the outer edge of the frame is measured first. For a standard curtain pair, each panel covers half the window width plus an overlap of 2 to 4 inches in the center. The finished curtain width per panel equals half the window width plus the overlap amount. For a single panel covering the full window, the full window width plus 2 inches for the overlap is used.
The finished length is measured from the rod position to the desired hem. For a sill-length curtain, the measurement runs from the bottom of the rod ring to 1 inch above the sill. For a floor-length curtain, the measurement runs from the rod ring to 0.5 inch above the floor. For a puddle-length curtain, an additional 6 to 10 inches beyond the floor is included. The finished length is recorded in inches.
Step 2: Apply the Pleat Ratio to Get the Cut Width
The pleat ratio is the multiplier that converts the finished curtain width into the flat fabric width before pleating. A standard pleat ratio is 2.0 for pencil pleat or pinch pleat. A lighter ratio of 1.5 works for eyelet curtains with less fullness. A heavy ratio of 2.5 or 3.0 provides a more luxurious drape for formal rooms.
The finished curtain width per panel is multiplied by the pleat ratio. The result is the cut width per panel in inches. For example, a finished panel width of 30 inches with a ratio of 2.0 results in a cut width of 60 inches. This cut width is compared to the fabric's usable width, usually 54 inches or 110 inches.
Step 3: Account for Pattern Repeat and Vertical Allowances
For patterned fabric, the pattern repeat is the vertical distance between one identical point on the design and the next. The repeat is measured by aligning two matching motifs on the fabric bolt. The finished length, hem allowance, and top heading allowance are added to get the basic cut length per panel. The hem allowance is typically 4 inches for a double-fold hem, and the top heading allowance is 3 to 5 inches depending on the curtain heading type.
The basic cut length is divided by the pattern repeat and rounded up to the nearest whole number. That whole number is multiplied by the pattern repeat to get the actual cut length per panel. For plain fabric, the actual cut length equals the basic cut length without rounding.
Step 4: Determine How Many Widths Each Panel Needs
The cut width per panel is compared to the fabric's usable width. If the cut width is less than or equal to the usable width, one width per panel is sufficient. If the cut width exceeds the usable width, fabric widths are joined. The cut width is divided by the usable width and rounded up to the next whole number. This is the number of fabric widths per panel.
When joining widths, 1 inch of seam allowance is added per join. For example, a cut width of 80 inches with a usable width of 54 inches requires 2 widths. The joined width becomes 54 plus 54 minus 1 inch for the seam, resulting in 107 inches, which is then trimmed to match the cut width. The extra fabric trimmed away adds to the total yardage requirement.
Step 5: Calculate Total Yardage Per Panel and for the Whole Curtain Set
The actual cut length per panel is multiplied by the number of widths per panel. This gives the total fabric length needed for one panel in inches. The value is divided by 36 to convert to yards. The result is rounded up to the nearest 0.25 yard for practical purchasing.
For a curtain pair, the per-panel yardage is multiplied by 2. For multiple windows, the per-window yardage is multiplied by the number of windows. If tiebacks are planned, 0.5 to 1 yard per pair of tiebacks is added. If the fabric has a large pattern repeat, an extra 0.25 to 0.5 yard per panel may be included to allow for pattern matching errors during cutting.
Step 6: Worked Example for a Patterned Curtain Pair
A window width of 48 inches is taken as an example. Each panel has a finished width of 26 inches (24 inches for half the window plus 2 inches for center overlap). A pleat ratio of 2.0 is used, so the cut width per panel is 52 inches. The fabric usable width is 54 inches, so one width per panel is enough. The finished length from rod to floor is 84 inches. Adding 4 inches for hem and 4 inches for heading gives a basic cut length of 92 inches. The pattern repeat is 12 inches. Dividing 92 by 12 gives 7.67, which rounds up to 8. Multiplying 8 by 12 gives 96 inches as the actual cut length per panel. Converting 96 inches to yards results in 2.67 yards per panel. For a pair, the total is 5.33 yards, rounded up to 5.5 yards.
Step 7: Worked Example for a Wide Window with Fabric Joins
A window width of 72 inches is taken as an example. Each panel has a finished width of 38 inches (36 plus 2). With a pleat ratio of 2.0, the cut width per panel is 76 inches. The usable fabric width is 54 inches, so 76 divided by 54 equals 1.41, which rounds up to 2 widths per panel. The joined width is 54 plus 54 minus 1 inch seam allowance, equaling 107 inches, and is trimmed to 76 inches. The finished length is 90 inches. Adding 4 inches hem and 4 inches heading gives a basic cut length of 98 inches. For plain fabric, the actual cut length is 98 inches. Multiplying 98 inches by 2 widths gives 196 inches per panel. Converted to yards, this is 5.44 yards per panel, rounded to 5.5 yards. For a pair, the total is 11 yards.
Step 8: Final Checklist Before Buying Fabric
The measured window width at three points (top, middle, and bottom) is confirmed, and the largest width is used for the calculation. The finished length is verified from the actual rod position, not from the window frame. The pleat ratio is decided based on the curtain heading style and the desired fullness. The pattern repeat is written down from the fabric label or by measuring the bolt. One inch per width join for seam allowance is included. Hem and heading allowances are included in every panel length. The final yardage is rounded up to the nearest 0.25 yard for each panel separately, and the panels are then added together. The fabric bolt width is checked before buying, as some fabrics have a usable width of 44 inches instead of 54 inches. A small fabric scrap is kept for future repairs or patch tests.