Curtain Calculation Formula — How to Calculate Fabric for Curtains

Q: What is the formula for calculating curtain fabric?

The curtain fabric calculation formula: Step 1) Window width × fullness ratio ÷ fabric width = fabric widths needed per panel (round up). Step 2) Finished drop + hem + header = cut length per panel. Step 3) Cut length × widths per panel × number of panels = total inches ÷ 36 = yards. Add 10% for waste.

The Curtain Fabric Calculation Formula

Calculating fabric for curtains is a two-step process: figure out how many fabric widths you need across the window, then calculate the total length. Here is the formula:

Step 1 — Widths Needed:
(Window Width × Fullness Ratio) ÷ Fabric Width = Number of Fabric Widths per Panel
Round up to the nearest whole number.

Step 2 — Yards Needed:
(Finished Drop + Hem Allowance + Header Allowance) × Number of Widths × Number of Panels ÷ 36 = Yards
Add 10% waste factor for shrinkage and cutting errors.

What Each Term Means

Term	Description	Typical Value
Fullness Ratio	How gathered the curtain looks when closed	2.0x (standard)
Fabric Width	The width of the fabric from selvage to selvage	54" (decor), 60" (wide), 108" (extra-wide)
Hem Allowance	Fabric folded under at the bottom	4" (double hem: 2" + 2")
Header Allowance	Fabric above the rod pocket or pleat tape	3"
Waste Factor	Extra fabric for shrinkage, pattern matching, mistakes	10%

Curtain Fabric Calculation Examples

Example 1: Standard Window (36" × 60")

Window: 36" wide, 60" drop. 1 panel. 2x fullness. 54" decor fabric. 4" hem, 3" header.

Width calculation: (36 × 2) ÷ 54 = 1.33 round up to 2 fabric widths

Length calculation: 60 + 4 + 3 = 67" per panel. Total: 67" × 2 widths × 1 panel = 134". 134 ÷ 36 = 3.72. With 10% waste: 4 yards (rounded to quarter yard).

Example 2: Patio Door (72" × 80", 2 panels)

Window: 72" wide, 80" drop. 2 panels. 2x fullness. 54" decor fabric.

Width calculation: (72 × 2) ÷ 54 = 2.67 round up to 3 fabric widths across both panels (1.5 widths each)

Length calculation: 80 + 4 + 3 = 87" per panel. Each panel needs 1.5 widths 87 × 1.5 = 130.5" per panel. For 2 panels: 261". 261 ÷ 36 = 7.25. With 10% waste: 8 yards.

Example 3: Floor-to-Ceiling (48" × 96", 2 panels, 108" extra-wide fabric)

Using 108" extra-wide fabric eliminates the need for multiple widths per panel.

Width calculation: (48 × 2) ÷ 108 = 0.89 round up to 1 fabric width. Perfect — one width covers the full window.

Length calculation: 96 + 4 + 3 = 103" per panel. For 2 panels: 206". 206 ÷ 36 = 5.72. With 10% waste: 6.25 yards.

Using the Formula with Our Calculator

The curtain fabric yardage calculator applies this formula automatically. You enter width, drop, fullness, fabric width, and allowances — the calculator handles width counts, rounding, waste factor, and provides both yards and meters.

For a free version with no sign-up, use the free curtain fabric calculator.

For metric measurements in cm and meters, use the curtain calculator in meters.

Frequently Asked Questions

What is the formula for calculating curtain fabric?

Step 1: Window width × fullness ÷ fabric width = fabric widths needed (round up). Step 2: (Drop + hem + header) × widths × panels ÷ 36 = yards. Add 10% waste.

How do you calculate fabric for bay window curtains?

Measure each bay window section separately — each angled section is an individual window. Apply the formula to each section and add the yardages together. Bay windows typically need 3-4 panels.

Does the formula change for lined curtains?

No — the formula is the same. You calculate face fabric yardage using the formula above, then buy the same amount in lining fabric. For blackout lining, add 2" to the hem allowance.

How does pattern repeat affect the formula?

Add the pattern repeat length to each panel's cut length before calculating. If pattern repeat is 12" and panel cut length is 67", use 79" as the cut length. This ensures pattern matches across panels.