Curtain Size Calculator

Curtain width = rod length × fullness (1.5 to 2.5), and curtain length = rod height minus the height of the hem. For a 48 in window with the rod 84 in off the floor, floor-length curtains need an 84 in drop and 120 in of total width, which is four ready-made 50 in panels when they are sold in pairs.

How the curtain size is calculated

Measure the window, decide where the rod goes and where the hem ends. Everything else follows from those three choices.

Rod length = window width + 2 × overhang; curtain width = rod length × fullness; panels = curtain width ÷ panel width, rounded up

• Overhang. The Shade Store puts the rod 6 to 12 in past the frame on an outside mount so the panels stack beside the glass. The calculator starts at 6 in.
• Fullness. Multiply the width the curtains must cover by 1.5 or 2 for a full look. The Shade Store gives 2.5 or 3 for sheers, and NICETOWN advises panels that add up to 2 to 2.5 times the window width.
• Rod height. Common practice is 4 to 6 in above the frame; the calculator uses 6 in. The Shade Store goes higher, up to two thirds of the way from the window to the ceiling, which makes a ceiling look taller and needs longer curtains.
• Length. Measure from the top of the rod (rings and clips shorten the fabric you need by 1 to 2 in, per NICETOWN).

Worked example: a 48 in window

Window 48 in wide and 48 in high, sill 30 in above the floor, rod 6 in above the frame, 6 in overhang, 2× fullness, panels 50 in wide:

1. Rod length: 48 + 6 + 6 = 60 in.
2. Curtain width: 60 × 2 = 120 in.
3. Panels: 120 ÷ 50 = 2.4, so 3 panels, and 4 when they are sold in pairs.
4. Rod height: 30 + 48 + 6 = 84 in from the floor.
5. Floor length: the hem stops 1/2 in above the floor, so the drop is 84 − 0.5 = 83.5 in, and the 84 in ready-made length fits.

Four 50 in panels are 200 in of fabric, a fullness of 3.3×. If you buy three single panels instead, you get 2.5×. Switch off "Sold in pairs" to see it.

Curtain length: sill, apron, floor or puddle

The four options are where the hem ends. The drop for the 48 in window above:

NICETOWN describes sill length as ending at the sill or up to 1/2 in above it, and apron length as 4 to 6 in below the frame (the calculator uses 5 in). A floor-length curtain floats about 1/2 in off the floor; a break adds 1 to 2 in, and a puddle is 2 to 4 in (NICETOWN) or 3 to 6 in (The Shade Store). The calculator uses 3 in for a puddle. Ready-made lengths come in 63, 84, 96, 108 and 120 in (The Shade Store): buy the next size up and hem the excess, or pick custom above 120 in.

Curtain size chart by window width

With a 6 in overhang, 2× fullness, 50 in panels and pairs, these are the results for a window 48 in high:

Drape size, inside mount and meters

"Drape size" is the same measurement: the width of fabric and the drop. For an inside mount the rod sits inside the frame, the rod length equals the window width and there is no overhang, so choose it with the Inside mount button. Curtains for a window that opens inward need the outside mount. To work in meters or centimeters, as most of the UK and Australia does, use the m · cm switch at the top of the calculator: every field, the diagram and the results change units and the maths stays the same.

What to plan next

Curtains are one part of the room. Size the rug under the seating, place the TV on the wall beside the window and pick the ceiling fan for the room. If you are repainting or papering the wall behind the rod, do that first: see the wallpaper calculator and the painting cost calculator. All tools are in room planning.