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Curtain Size Calculator
Use this free curtain size calculator to get the right curtain size for any window. Enter the window width and height, pick a fullness factor, and it works out each panel width, the finished curtain length, the rod length, and how many yards of fabric to buy.
Measure the window frame, not the glass. The top allowance covers the rod pocket or header above the window; the hem allowance is the fold at the bottom.
| Amount | Value |
|---|---|
| Total fabric width (width × fullness) | 96 in |
| Width per panel | 48 in |
| Finished curtain length | 68 in |
| Rod or track length | 56 in |
| Fabric needed (54 in wide fabric) | 3.4 yards |
| Fabric needed (45 in wide fabric) | 4.0 yards |
How it works
Curtains that are exactly the width of the window look flat and stretched when they are closed, and skimpy when they are open. The secret to curtains that look right is fullness: the fabric should be wider than the window, so it falls in soft folds. This calculator turns your window measurements into panel sizes, a finished length, a rod length, and the yardage to buy.
Fullness is a multiplier on the window width. A factor of 1.5 gives a light gather, good for sheer curtains and casual rooms. A factor of 2 is the standard choice for most curtains — the fabric is twice as wide as the window, so the folds look full without being heavy. A factor of 2.5 gives a lush, formal look, and 3 is for very full sheers or layered looks. Multiply the window width by the fullness, then divide by the number of panels, and you have the width of each panel. A 48-inch window at 2× fullness needs 96 inches of fabric in total, or 48 inches per panel if you hang two panels.
Width per panel = total fabric width ÷ number of panels
Finished length = window height + hem allowance + top allowance
Rod length = window width + 8 inches (4 inches of overhang each side)
The finished length is the window height plus two allowances. The hem allowance, usually 4 inches, is the fold at the bottom of the curtain; a generous hem helps the curtain hang straight and lets you lengthen it later. The top allowance, usually 4 inches for a rod and 2 inches for a track, covers the header or rod pocket above the window. With a 60-inch window, a 4-inch hem, and a 4-inch top allowance, the finished length is 68 inches.
The rod should be longer than the window so the curtains can stack to the sides and leave the glass clear when they are open. Adding 4 inches of overhang on each side, or 8 inches in total, is the usual rule: a 48-inch window takes a 56-inch rod. If you want the curtains to puddle on the floor, add 2 to 6 inches to the length; if you want them to just brush the floor, keep the length as calculated; for a sill-length curtain, measure to the sill instead of the floor.
Fabric yardage depends on the width of the fabric roll. Most home fabric is 54 inches wide; some is 45 inches. The calculator divides the total fabric area by the roll width and converts to yards, so you know how much to buy. Always round up and buy an extra half yard for matching patterns or fixing mistakes — patterned fabric needs extra for matching the repeat across panels.
Worked example
You have a window that is 48 inches wide and 60 inches tall. You want standard fullness, two panels, a curtain rod, a 4-inch hem, and a 4-inch top allowance.
Step 1: Total fabric width — 48 × 2 = 96 inches.
Step 2: Width per panel — 96 ÷ 2 panels = 48 inches per panel.
Step 3: Finished length — 60 + 4 (hem) + 4 (top) = 68 inches.
Step 4: Rod length — 48 + 8 = 56 inches.
Step 5: Fabric yardage — 96 × 68 = 6,528 square inches; at 54 inches wide that is 6,528 ÷ 54 ÷ 36 = 3.4 yards.
The result is 48 inches wide × 68 inches long per panel, on a 56-inch rod, needing about 3.4 yards of 54-inch-wide fabric. That is exactly what the calculator shows for these inputs.
FAQ
How wide should curtains be for a 48-inch window?
For a 48-inch window at standard 2× fullness, you need 96 inches of fabric in total — two panels of 48 inches each. At light 1.5× fullness you need 72 inches in total, and at lush 2.5× fullness you need 120 inches. Curtains exactly the width of the window look flat and stretched, so always buy wider than the window.
What is fullness in curtains?
Fullness is how much wider the curtain fabric is than the window. A fullness of 2× means the fabric is twice as wide as the window, which creates the soft folds you see on well-hung curtains. Light sheers use 1.5×, standard curtains use 2×, and formal or very full curtains use 2.5× or more.
How long should curtains be?
It depends on the look you want. For floor-length curtains, measure from the rod to the floor and add the hem and top allowances — the calculator does this for you. Curtains that just brush the floor are the safest choice; adding 2 to 6 inches makes them puddle on the floor, which looks formal but collects dust and is a trip hazard with pets or small children.
Should the curtain rod be wider than the window?
Yes. The rod should extend about 4 inches past the window frame on each side, so 8 inches wider in total. That lets the curtains stack to the sides of the window when open, instead of blocking the glass. For a 48-inch window, use a 56-inch rod.
How much fabric do I need for two curtain panels?
Multiply the window width by your fullness factor, multiply by the finished length, and divide by the fabric roll width. For a 48 by 60 inch window at 2× fullness, that is about 3.4 yards of 54-inch-wide fabric. Buy an extra half yard if the fabric has a pattern, so the pattern matches across both panels.