About 2× the width of your curtain rod. Total panel width should equal rod length multiplied by your fullness ratio. A 48-inch rod with 2× fullness needs 96 inches of total fabric — typically split into two 50-inch panels for a properly gathered look.

They end at progressively lower points. Sill ends at the windowsill, apron extends 4″ below the sill, floor stops ½″ above the floor, and puddle pools 6″ on the floor. Floor length is the most common modern choice; puddle reads as more formal.

Outside mount in almost all cases. Mounting the rod above and beyond the frame makes windows look larger, lets in more light, and gives proper room for fullness. Use inside mount only when you want a clean, recessed look and the window frame is deep enough.

4 to 6 inches above the frame is standard. For higher ceilings, hang the rod 8–12 inches above — or halfway between the window top and the ceiling — to make the window look taller. Avoid hanging the rod directly on the frame; it visually shrinks the window.

4 to 10 inches per side, with 6 inches as the standard. Extending the rod past the frame lets open curtains clear the window completely, so you get full daylight and the window looks wider. For statement windows, go up to 12 inches per side.

Fullness is total fabric width divided by rod length — and the standard is 2×. A 2× ratio gives proper gathered folds without looking sparse. Use 1.5× for sheers or minimalist looks, and 2.5–3× for a luxurious, drapery-store finish.

Two panels for most standard windows. A single panel works for narrow windows where the curtain stays open to one side. Use four panels on wide windows (over 72 inches) or sliding doors so each pair stacks neatly on either side.

Multiply finished panel length by the number of panels. Standard fabric is 54″ wide, so most single panels need one fabric width per panel. Add 8″ to length for top and bottom hems, and 4″ to width per panel for side hems before cutting.