Decide curtain type: full-length, floor-length, or sill-length
Choose rod/track position and measure the mounting height
Measure curtain width (for fullness)
Measure the window width (inside frame or outside trim—use the same reference for all measurements)
Multiply window width by the fullness factor:
5–2.0 for light/standard fullness
0–2.5 for full/very full pleats
5–3.0 for very dramatic fullness (if using heavy fabrics/large gathers)
Add overlap/coverage if needed:
Add 2–6 in (5–15 cm) total for center overlap (or as required for your style)
Add extra width for tiebacks/side panels if applicable
Measure curtain drop length
From the top of the rod/track (or desired curtain top) to the desired bottom point:
Sill-length: bottom at window sill
Puddle length: 0–1 in (0–2.5 cm) above floor or slight “break”
Floor-length: 1–2 in (2.5–5 cm) above floor for clearance
Touching/stacking: follow the manufacturer’s guidance for your fabric and hem type
If using rings/hooks, include the ring/hook height and any header/rod clearance
Account for curtain top style
If using grommets: measure from rod center to desired bottom (or use manufacturer chart)
If using pinch pleats/rod pocket: measure from the top seam/header position to desired bottom
If using a custom header/valance: measure separately for each section
If using two panels
Divide the total measured curtain width by 2 for equal panels (use the same fullness total you calculated)
Ensure each panel width includes any overlap needed
If installing inside the window frame (inside mount)
Measure inside width at the narrowest point
Measure inside height at the left, center, and right; use the smallest measurement
Check for obstructions (sill molding, crank handles, trim)
If installing outside the window frame (outside mount)
Measure from where the rod/track will be mounted to the desired curtain bottom
Measure the rod/track width to ensure adequate coverage beyond the window edges
Add extra side coverage beyond the window width as needed (commonly 4–12 in total, depending on style)
Record measurements clearly
Write: width reference (inside/outside), total curtain width, number of panels, and final length from rod/track to bottom
Measure twice (left/right heights and any uneven window frames)