πͺ Curtain Size Calculator
Get the perfect curtain width, length, and rod size for any window.
Recommended Panel Width (2 panels)
How to Use This Calculator
This calculator gives you the three numbers that matter for curtains: how wide each panel should be, how long the drop should be, and what size rod to buy, based on your window, mount type, hanging style, and fullness.
Measure the window width and height in inches. For an outside mount, measure including the trim; for an inside mount, measure the inside of the frame.
Choose the mount type. Outside mounts are the most common and make windows look larger; inside mounts sit within the frame for a tidy minimal look.
Pick a hanging style: sill, apron, floor, or puddle. Floor length is the safest default for living rooms and bedrooms.
Choose fullness: 2x for classic folds. Read the panel width, total fabric width, rod length, drop length, and fabric yardage from the results.
Width, Rod, and Fullness Explained
Fullness is what creates folds. Flat 1.5x fabric barely ripples, which suits modern tailored rooms; 2x gives the soft classic gather most people picture; 2.5x to 3x gives deep luxurious folds for formal rooms and helps blackout linings hang properly. The total fabric width is normally split into two panels, one per side. For the rod, an outside mount adds about 10 inches total so the open panels stack on the wall beside the glass instead of blocking light. Hang the rod 4 to 6 inches above the frame: the extra height draws the eye up and makes the window feel taller.
Worked Example
A 36 by 48 inch window, outside mount, 2x fullness, floor-length style. Total fabric width = 36 x 2 = 72 inches, so each of the two panels should be 36 inches wide. Rod length = 36 + 10 = 46 inches. Drop = 48 + 29 = 77 inches. Fabric needed = (72 x 77) / 1296 = 4.28 square yards. Switch the style to sill length and the drop becomes 48 + 9 = 57 inches, with the same 36-inch panels and 46-inch rod.
Hanging Styles and the Assumptions Behind the Numbers
Drops are measured from the rod, not from the top of the window, so the calculator bakes in standard rod placement. The assumptions: for an outside mount the rod sits 5 inches above the window top; sill length ends 4 inches below the sill; apron length ends 10 inches below the sill; floor length assumes 24 inches from the window bottom to the floor, which fits a standard window on an 8-foot wall; puddle adds 8 inches of pooling fabric to the floor length. If your window sits much higher or lower, measure the real rod-to-floor distance and adjust.
A few pro rules round this out. Panels should never look stretched flat when closed; if in doubt, go up one fullness step. For wide windows or sliding doors, consider three or four panels instead of two so the stack does not get bulky on one side. Match the rod diameter to the weight: sheers are fine on slim rods, but 3x blackout panels need a thick rod with center support brackets on spans over 48 inches. And always buy the rod before the curtains, because finials and brackets change the effective hanging width.
Frequently Asked Questions
How wide should curtains be compared to the window?
Multiply the window width by a fullness factor: 1.5x for a flat tailored look, 2x for classic soft folds (the most popular choice), 2.5x for a lush look, and 3x for blackout or heavy fabrics that need deep gathers. That total fabric width is usually split across two panels, so each panel is half the total. Skimpy panels that barely cover the window are the most common curtain mistake.
Should curtains end at the sill or the floor?
Floor length looks best in living rooms and bedrooms: the hem should just kiss the floor or hover half an inch above it. Sill length (ending just below the sill) suits kitchens and bathrooms where fabric near the floor would get dirty or block radiators. Apron length, ending a few inches below the sill, is a middle ground for casual rooms. Puddling, with extra inches pooling on the floor, is a formal look for low-traffic rooms.
What is curtain fullness?
Fullness is the ratio of total fabric width to the width it covers. A 2x fullness on a 36-inch window means 72 inches of fabric gathered onto 36 inches of rod, which creates the folds. Higher fullness gives deeper, richer folds but needs a sturdier rod and more stacking space at the sides. Sheers can go up to 3x because the fabric is so light.
How high should the curtain rod hang?
For an outside mount, hang the rod 4 to 6 inches above the window frame and extend it 4 to 5 inches past the frame on each side. The extra height makes windows look taller, and the extra width lets panels stack clear of the glass so you get full light when they are open. Inside mounts sit within the frame itself, which suits a clean minimal look.
How do I measure for an inside vs outside mount?
For an inside mount, measure the exact inside width of the window frame; the rod and panels fit within it, so order the rod to that width. For an outside mount, measure the full window width including trim, then add about 10 inches total (5 per side) for the rod so stacked panels clear the glass. Measure drop from where the rod will sit, not from the top of the window.