Calculators
Curtain and rod size calculator
Curtains fail on two numbers: hung too low, and bought too narrow. Both are avoidable with a tape measure and five minutes.
On this page (3 sections)
Short answer
Mount the rod 4 to 6 in (10 to 15 cm) above the trim at minimum, or within 2 to 4 in (5 to 10 cm) of the ceiling when the gap is under a foot. Extend it 4 to 10 in (10 to 25 cm) past each side, and buy 2 to 2.5 times the rod width in flat fabric.
The numbers, at a glance
- Rod above trim, minimum
- 4 to 6 in (10 to 15 cm)
- Extension each side
- 4 to 10 in (10 to 25 cm)
- Fullness
- 2x standard, 2.5x pleated
- Standard panel width
- 50 in (127 cm)
Curtain and rod size calculator#
Gives rod width, mounting height, how much fabric you need for a real gather, and the finished panel length for the hem you want.
Nothing you type leaves your browser: the maths runs on this page, and no values are stored or sent anywhere.
The three decisions, in order#
Height. The calculator places the rod about 55% of the way up the wall above the trim, never closer than 4 in (10 cm) to the ceiling. If the wall above the trim is less than 12 in (30 cm), it goes straight to a ceiling-adjacent position, because a rod squeezed into a small gap draws attention to the gap.
Width. Extension is calculated as the larger of 6 in (15 cm) and 16% of the window width, when you tell it the panels have to clear the glass. That percentage is a working approximation of stack-back for a pair of panels at 2x fullness. Decorative panels that never move need only 4 to 5 in (10 to 13 cm).
Length. Finished panel length is the rod height minus about 1.5 in (4 cm) for rings, adjusted for the hem position you choose. The result is the length you order for made-to-measure, or the length you hem a ready-made down to.
What changes with heading type#
| Heading | Stack as a share of flat width | Notes |
|---|---|---|
| Grommet / eyelet | About 1/4 | Tightest stack, coarse fold, needs 2x minimum |
| Pinch pleat | About 1/3 | Deepest fold, widest stack, the most tailored |
| Wave / ripplefold | About 1/4 to 1/3 | Very predictable, needs its own track |
| Rod pocket | About 1/3 | Does not slide well, best for static panels |
| Tab top | About 1/4 | Casual, and the tabs catch on the rod |
Before you order#
- Measure the rod position after you fix the brackets, not before. The panel length depends on the rod, not on the window.
- Check the floor level at both ends of the window. A 3/4 in (2 cm) fall across a 90 in run is common in older houses and shows badly on a kissing hem.
- Allow for a shade or blind underneath: the rod needs 3 to 5 in (8 to 13 cm) of projection to clear it.
- If you are between ready-made lengths, buy long and hem. Buying short is unrecoverable.
Frequently asked questions#
How high should curtains be hung?
At least 4 to 6 in (10 to 15 cm) above the window trim, and usually about halfway between the trim and the ceiling. When there is less than 12 in (30 cm) of wall above the trim, mount within 2 to 4 in of the ceiling or use a ceiling-fixed track.
How wide should a curtain rod be?
The window width plus 8 to 20 in (20 to 51 cm) in total. The driver is stack-back: the panels have to sit off the glass when open, and a pleated panel stacks to roughly a third of its flat fabric width.
Why is the rod so much wider than my window?
Because the panels have to go somewhere when they are open. That stack-back is roughly a third of the flat fabric width for a pleated heading, so a pair on a 48 in (122 cm) window needs about 8 in (20 cm) of wall on each side before any of the glass stays clear. Tell the calculator the panels are decorative and it drops the extension to 5 in (13 cm).
Should I order the exact panel length the calculator gives?
For made-to-measure, yes. For ready-made, buy the next standard length up (84, 96, 108 or 120 in) and hem down to the figure. Hemming is straightforward and reversible; a panel that arrives 2 in short is unrecoverable.
Sources and standards referenced#
- Soft furnishings workroom practice Trade practice, UK and US drapery workroomsFullness ratios, stack-back allowances and heading types
- Architects' Data Ernst NeufertWindow and reveal dimensions
We cite published codes, industry planning guidelines and manufacturer specifications. Where a figure is our own recommendation rather than a published standard, the text says so. See how we measure.