Professional-grade curtain calculator: compute total fabric width, panel cuts, required yardage, fullness ratio, and grommet count. Includes interactive diagram based on your window dimensions — ideal for designers, DIYers, and home renovators.
Getting curtain dimensions right transforms a room. The fullness ratio (gathering factor) determines how pleated or flat the drapes appear — standard pinch pleat drapery uses 2.0x to 2.5x the rod width. Our calculator applies industry-accepted formulas: Rod Width = Window Width + (2 × Side Extension). Then Total Fabric Width = Rod Width × Fullness Ratio. Based on your fabric’s selvedge width, we compute how many vertical panels (widths of fabric) are required and the exact cut width per panel.
Core Equations
Rod Width = WinWidth + 2×Extension
Fabric Width Total = Rod Width × Fullness
Number of Panels = ceil(Fabric Width Total / Fabric Width)
Cut Width per Panel = (Fabric Width Total + seam_allowance) / Panels
Cut Length = Desired Drop + Hem Allowance
Additionally, the calculator estimates ring/grommet count based on rod width divided by typical spacing (12 cm is standard). For traverse rods or back tabs, adjustments may be needed. We incorporate extra seam allowance for side hems and panel joining.
Step 1 — Measure window width: Use a steel tape to measure the exact width of the window frame. Add side extension (typically 15–30 cm each side) so curtains can be drawn completely clear of glass, maximizing light and view.
Step 2 — Determine drop length: Decide if you want sill-length (just below sill), apron (below sill by 10–15cm), or floor-length (1–2 cm above floor). For floor-length, measure from the top of the rod (or ring) to floor level, then subtract 1–2 cm for clearance. Our drop length field should reflect rod-to-hem distance.
Step 3 — Choose fullness factor: Lightweight sheers require 2.5–3x fullness for airy folds. Medium weight cotton/poly blends work well with 2–2.2x. Heavy velvet or blackout can use 1.8–2x to avoid excessive bulk.
Step 4 — Fabric width: Standard decorator fabric is 140cm wide. Wide-width fabrics (280cm) reduce seams and are great for high windows. Account for pattern repeat if applicable (not included but recommended).
| Parameter | Description |
|---|---|
| Total Rod Width | Final width the curtain will cover (window + side extensions). |
| Total Fabric Width (fullness) | Total width of flat fabric needed before gathering, including pleats. |
| Number of Panels | How many fabric widths (vertical strips) to sew together per curtain (or pair). |
| Cut Width per Panel | Width to cut each fabric piece, includes seam allowance if multiple panels. |
| Cut Length | Length to cut each drop = finished length + hem allowance. |
| Total Yardage (meters) | Total fabric required in linear meters (based on cut length × number of widths). |
A client with a window width of 210 cm, side extension 20 cm each side (rod width = 250 cm). Fullness ratio = 2.2 → total fabric width = 550 cm. Fabric width 140 cm → 4 panels (ceil(550/140)=4). Cut width per panel = (550 + 6cm seam allowance)/4 ≈ 139 cm each. Drop length = 245 cm from rod to floor, hem allowance 20 cm → cut length = 265 cm. Total fabric needed: 4 × 2.65 m = 10.6 meters. This calculator returns precise figures, helping the homeowner order exactly 11 meters (with buffer).