Curtain Size Calculator

Article — Curtain Size Calculator

Curtain Size Calculator

For a tailored modern look, curtain width should be 1.5 to 3 times the window width — most rooms land at 2×. Length depends on where you want the hem: at the sill, just below it, kissing the floor, or puddled. Mount the rod 4 to 6 inches above the window and add 8 to 12 inches on each side.

The width-times-fullness math is what makes curtains look intentional rather than droopy or stretched. A window that gets a flat panel exactly its own width ends up looking like a sheet held up by clips. A window that gets 2 to 2.5 times its width in fabric gets the even folds you see in furniture-store photography. Length picks the room's formality.

What curtain size do I need?

For an outside-mount installation, total curtain width should be twice the rod width, and the rod width should be the window width plus 16 to 24 inches (8 to 12 inches per side). Length should reach the floor for living rooms and bedrooms, or stop at the sill for kitchens and bathrooms. Two panels is the standard count — one on each side of the window.

The single most common sizing mistake is buying curtains the same width as the window. Without extra fullness, the panels look stretched flat with no folds. Without side margin, the rods do not extend past the glass, so the curtains never fully clear the window when open. Both mistakes are easy to fix with the right curtain size calculation before ordering.

Curtain width and the fullness ratio

Fullness ratio is the multiple of fabric to rod width. A 2× fullness means the panels, laid flat, are twice as wide as the rod is long. When gathered onto the rod, that extra fabric becomes folds. More fullness gives deeper, more even folds at the cost of more fabric.

• 1.5× fullness — light, casual; works for sheer panels and lightweight cotton.
• 2× fullness — standard; balanced folds for most living rooms and bedrooms.
• 2.5× fullness — full; deeper folds for formal rooms or thicker fabrics.
• 3× fullness — luxury; dense folds for sheers, ballrooms, or hotel suites.
• Heavier fabrics — can go down to 1.5× because they already fold under their own weight.

Curtain length styles: sill to puddle

Curtain length sets the formality of a room. Four standard styles are recognized by interior designers: sill, below-sill (apron), floor-length, and puddled.

Sill-length is the casual choice — kitchens, bathrooms, breakfast nooks. Apron drops are a hand-me-down from rental apartments; they rarely look intentional. Floor-length is the default for any room you want to feel finished. Puddled is back in fashion in maximalist interiors after a decade in the wilderness.

Inside vs outside mount curtains

Inside mount means the rod sits inside the window casing. Outside mount means the rod sits on the wall above the window. The two looks are quite different.

Inside mount is the choice when the window casing is beautiful enough to display, or when wall space above the window is limited. The tradeoff is reduced fullness — the casing limits how much fabric you can gather. Outside mount lets you go to 2.5× or 3× fullness and is the default for most living and sleeping rooms.

How to measure a window

For outside mount, measure the window width plus 8 to 12 inches on each side, and the height from the rod position to where you want the hem. The rod typically goes 4 to 6 inches above the window trim — higher if you want the window to feel taller. For inside mount, measure the inside dimensions of the casing at three points and use the smallest.

Standard ready-made panel sizes

Ready-made panels at US retailers (West Elm, Pottery Barn, Crate & Barrel, Target, IKEA) come in standard widths of 50 to 54 inches and standard lengths of 63, 84, 95, 108, and 120 inches. Two panels paired on a window give a total width of 100 to 108 inches, which covers an outside-mount rod up to about 50 inches at 2× fullness.

Length picks up at 84 inches for a standard 8-foot ceiling with an above-window mount, 95 inches for a 9-foot ceiling, and 108 inches for a 10-foot ceiling. Round up if your measurement falls between sizes — a hem is easy to shorten, but you cannot add length. For non-standard heights, custom drapery starts around three times the price of ready-made.

Hanging higher and wider

Two tricks change how a window looks without changing the window itself. Mounting the rod higher than the trim makes the window appear taller. Mounting it wider on the sides — and letting the panels stop just past the window glass — makes the window appear wider. Both work because the eye reads the rod-to-rod span as the window.

For the tall trick, mount the rod halfway between the window and the ceiling. For the wide trick, plan 8 to 12 inches of overlap per side. Together, they can make a small awkward window read as a large balanced one. The calculator's outside-mount option includes both adjustments by default.

Curtain size mistakes to avoid

Three mistakes account for most curtain regret. First: panels exactly the window width. This is the look that makes curtains feel cheap. Second: rod at the same height as the window trim. The window looks shorter than it is. Third: hem floating four inches above the floor. This is the "high-water" look — usually the result of buying the next size down to save money.

A fourth, less obvious one: heavy fabric at high fullness. Velvet at 3× fullness is impressive in a hotel ballroom and impossible to draw in a normal bedroom. Match the fullness to the fabric weight. Sheers and cottons take 2× to 3×. Linens and lined cottons take 2× to 2.5×. Velvets and blackout fabrics take 1.5× to 2×.