Calculator
Curtain size calculator
Measure the window frame, the floor to the top of the frame and the ceiling, then get a rod height, a rod width, a finished curtain length and a panel count. It updates as you type and nothing leaves your device. Use inches or centimeters.
4 panels, 96 in long (rod 60 in wide)
Worked example (shown when scripts are off): a 48 in wide window with the frame top 80 in from the floor, in a room with an 8 ft ceiling. The rod goes about 85 in from the floor and is 60 in wide. The curtains must be about 84.5 in long, so a 96 in ready-made panel is the nearest long enough, hemmed up by about 11 in. At twice the rod width you need about 120 in of fabric, which is four panels of 50 in.
Before you buy
Hang the rod first, then measure from the rod or the bottom of the rings to the floor. A finished curtain is easier to shorten than to lengthen.
How the calculator works
The rod goes about 4 to 6 in above the window frame, or close to the ceiling, which makes the window look taller. The calculator uses 5 in for the first choice and 3 in below the ceiling for the second, and never puts the rod above the ceiling. The rod is wider than the frame by the amount you choose on each side, so the curtains stack beside the window and the glass stays clear when they are open.
Finished length is the rod height minus the gap at the floor: half an inch for a clean hover, nothing for curtains that just touch, and 3 in extra for a puddled look. The calculator then names the nearest common ready-made length that is long enough from 84, 96, 108 and 120 in. If your length is a little shorter, the curtain can be hemmed up. Panels longer than 120 in need made-to-measure or extra-long sizes.
For width, the total fabric is the rod width times the fullness. A factor of 2 is the usual rule for a gathered look, 1.5 is flatter, and 2.5 is fuller. The total divided by the panel width, rounded up to a pair, gives the number of panels. Many ready-made panels are about 50 in wide, but check the label, because some quote the width before gathering.
Worked example
Take a 72 in wide window with a frame top at 80 in and a 9 ft ceiling (108 in), with the rod near the ceiling. The rod is at 105 in, the rod width is 84 in with 6 in on each side, and the length is 104.5 in. The nearest long enough ready-made length is 108 in. At twice the rod width, 168 in of fabric needs four panels of 50 in. The same window with a standard rod height at 85 in needs only a 96 in length, so a higher rod needs longer panels and costs more.
Limits
- It assumes a straight rod across a single window on a flat wall. Bay windows, sloped ceilings, radiators under the window and door swings need a hand measurement.
- Rings, clips, pleat tape and rod style add or remove an inch or two of drop, so allow for hardware.
- Curtain cords and blind cords are a strangulation risk for young children. Keep cords out of reach, and check current safety guidance if there are small children in the home.
- This is general information, not professional advice. For heavy or lined drapes, follow the instructions for the rod and the wall fixings.
Where this comes from
The rod height, rod width and floor-gap rules match the window treatment advice in the small-room guide on this site, which cites a rod near the ceiling or 4 to 6 in above the frame, and curtains extending a few inches past each side. We also read several general home design guides on curtain length and fullness, which agree on a fullness of about 2 and on the hover, touch and puddle options. Ready-made lengths of 84, 96, 108 and 120 in are the common sizes sold in North America. The 5 in and 3 in choices are our own simplifications.