Curtain Size Calculator: Rod, Panel Width and Length
Size curtains from the rod, not the window glass. The rod runs 6 to 12 inches past each side of the window frame; the panels together should be 1.5 to 2 times the rod width for standard curtains (2.5 times for pleated drapery), then you pick a length: sill, apron (4 to 6 inches below the sill), floor, or a puddle. Enter your window below to get every number.
Curtain size calculator
Enter your window and how you want the curtains to hang. Results update as you type and the numbers are saved in the page address. Nothing leaves your browser. Everything is in inches.
How the curtain calculator works
It sizes the rod first, multiplies by the fullness for your style to get the total fabric width, divides that between your panels, and then measures each length option from the top of the rod.
rod width = window width + 2 × rod extension total fabric = rod width × fullness panel width = total fabric ÷ number of panels rod height = floor to window + window height + rod above the frame sill length = rod above the frame + window height apron length = sill length + 4 to 6 in floor length = rod height − 0.5 in puddle length = rod height + 1 to 3 in (sweep) or 6 to 12 in (puddle)
- fullness
- 2 for standard curtains, 2.5 for pleated drapery
- lengths
- all measured from the top of the rod
Worked example
Given: window 36 in wide and 60 in high; bottom of the window 30 in from the floor; rod 6 in above the frame, 6 in past each side; standard curtains at 2 times fullness, two panels.
- Rod width:
36 + 2 × 6 = 48 in - Total fabric:
48 × 2 = 96 in - Each panel:
96 ÷ 2 = 48 in wide - Rod height from the floor:
30 + 60 + 6 = 96 in - Sill length:
6 + 60 = 66 in - Apron length:
66 + 4 to 6 = 70 to 72 in - Floor length:
96 − 0.5 = 95.5 in - Puddle length:
96 + 1 to 3 = 97 to 99 in for a sweep, up to 108 in for a dramatic puddle
Answer: A 48 in rod, two panels each 48 in wide, and a floor length of about 95.5 in (a ready-made 96 in panel is the nearest size, before the drop of your rings or clips).
Published ratios used
| Item | Rule | Source |
|---|---|---|
| Rod past each side of the window | 6 to 12 in | Source 1 |
| Goblet pleat drapery fullness | about 2.5 times the rod width | Source 1 |
| Standard curtains fullness | 1.5 to 2 times the rod width | Source 2 |
| Blackout panels | 1.5 times the rod width | Source 2 |
| Sheers | 2 to 2.3 times the rod width | Source 2 |
| Apron length | 4 to 6 in below the sill | Source 2 |
| Floor length for frequently used curtains | about 0.5 in off the floor | Source 1 |
| Soft sweep or puddle | 1 to 3 in (sweep) or 6 to 12 in (dramatic) past the floor | Source 2 |
| Rod height, high ceilings | 6 to 10 in above the window frame | Source 2 |
| Common ready-made lengths | 63, 84, 95 or 96, 108 and 120 in | Source 2 |
These are makers' guidelines for appearance and function, not standards. The Shade Store also lists 1 in to 6 in for a small puddle or break; the choices above come from the two guides listed.
Assumptions and limits
- Lengths are measured from the top of the rod. Subtract the drop of your rings, clips or tabs; add an inch or so for a rod pocket.
- Standard curtains use the top of the 1.5 to 2 times range (2 times). Choose blackout for 1.5 times.
- The rod height default of 6 in is the low end of a high-ceiling suggestion and a planning default for other rooms.
- Panel widths are the finished width of fabric before any header gathers. Round up to the next available panel size.
- Figures as published on 2026-11-13.
Frequently asked questions
How wide should curtains be for my window?
Measure the rod, not the glass. The Shade Store recommends the rod extend 6 to 12 inches past each side of the window or door, so rod width is the window width plus 12 to 24 inches. The total width of all panels should be about 1.5 to 2 times the rod width for standard curtains, per Two Pages Curtains.
What is fullness and how much do I need?
Fullness is the extra fabric that makes folds when the curtains are closed. Two Pages Curtains lists 1.5 to 2 times the rod width for standard curtains, 1.5 times for blackout panels and 2.3 times as the top of its range for sheers. The Shade Store builds its goblet pleat drapery at about 2.5 times. Lighter fabrics need more fullness to avoid looking limp.
What are sill, apron, floor and puddle lengths?
Sill length ends at the window sill. Apron length ends 4 to 6 inches below the sill. Floor length ends just above the floor; for curtains that open and close often The Shade Store suggests about 0.5 inch off the floor. A puddle extends past the floor: 1 to 3 inches for a soft sweep or 6 to 12 inches for a dramatic, luxurious look (Two Pages Curtains).
How high should I hang the rod?
That is your choice and depends on the room. Two Pages Curtains suggests 6 to 10 inches above the window frame in rooms with high ceilings to raise the ceiling line. The calculator starts at 6 inches; change it to see the effect on length.
How many panels do I need?
Two panels, one on each side, is the usual choice for a window that opens and closes, and the calculator divides the total fabric width between them. Choose one panel only if the curtain stacks to one side, and it carries all the fabric.
Which ready-made length should I buy?
Ready-made curtains commonly come in 63, 84, 95 or 96, 108 and 120 inch lengths, but sizes vary by brand. The calculator shows the nearest length below and above your result. A panel that is too short looks like high-water pants; a little too long can be hemmed or can puddle.
Do rings and clips change the length?
Yes. The length here is from the top of the rod. Curtains hang from rings, clips or a rod pocket, which sit a little above or below the rod. The Shade Store publishes a deduction chart of about 1 to 3.5 inches for its own hardware, so check yours and adjust.
Sources
- The Shade Store, Goblet Drapery Measure Instructions (rod extension, fullness, floor and puddle tips) (theshadestore.com) Accessed 2026-11-13. The Shade Store makes custom drapery.
- Two Pages Curtains, Curtain Sizes Guide (fullness table, length types, ready-made lengths, rod height) (twopagescurtains.com) Accessed 2026-11-13. Two Pages Curtains is a curtain maker.