Curtains are usually mounted 4–6 in above the window frame and extend 3–8 in beyond each side so they do not block light when open. Floor-length curtains should just kiss the floor; “puddled” curtains add 6 in or more.
How to use the Curtain Size Calculator
- Curtain style
- Fullness
- Window drop (top of frame to sill, apron or floor)
- Window width (including overlap)
- Rod allowance above frame
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the curtain style and fullness, and enter the window height (from where the rod will go to the sill, apron or floor) and width.
Tips
- Measure over thin clothing with a soft tape held snug but not tight, and keep the tape level all the way round.
- Take each measurement twice; if you are between sizes, the larger size is usually the safer choice.
- Size charts vary by brand and country – check the maker’s own chart when it is available.
- For sewing projects, pre-wash fabric before cutting and buy 10% extra for shrinkage, pattern matching and mistakes.
Common mistakes to avoid
- Mixing inches and centimetres between the tape and the size chart.
- Forgetting seam and hem allowances when cutting fabric.
- Measuring an old, stretched garment instead of your body.
Inputs explained
| Field | What to enter |
|---|---|
| Curtain style | Choose one: Sill length, Apron length, Floor length, Café (half height) … |
| Fullness | Choose one: Standard (2×), Deluxe (2.5×), Ultra (3×) |
| Window drop (top of frame to sill, apron or floor) | Units: in, cm |
| Window width (including overlap) | Units: in, cm |
| Rod allowance above frame | Units: in, cm |
What each result means
- Total curtain width = [Window width (including overlap)]×[Fullness]
- Width of each of two panels = [Total curtain width]÷2
Example values
How the main result changes when Window drop changes and everything else stays at the example values above:
| Window drop (top of frame to sill, apron or floor) (in) | Curtain length (in) |
|---|---|
| 40 | 44 |
| 60 | 64 |
| 80 | 84 |
| 100 | 104 |
| 120 | 124 |
| 160 | 164 |
Formula
Length: sill/apron/floor = window drop + 4 in rod allowance (+ 6 in extra-long); café = half the window heightWidth = window width (plus overlap) × fullness (2, 2.5 or 3)Worked example
Inputs — Curtain style: Floor length; Fullness: Standard (2×); Window drop (top of frame to sill, apron or floor): 80 in; Window width (including overlap): 48 in; Rod allowance above frame: 4 in.
Results — Curtain length = 84 in; Total curtain width = 96 in; Width of each of two panels = 48 in.
Frequently asked questions
How wide should curtains be?
Two to three times the width of the window (including overlap) so they look full when closed.
How high should a curtain rod be?
About 4–6 in above the window frame, or halfway between frame and ceiling to make the window look taller.
What length are standard ready-made curtains?
63, 84, 95, 108 and 120 in in the U.S.
What formula does the Curtain Size Calculator use?
Length: sill/apron/floor = window drop + 4 in rod allowance (+ 6 in extra-long); café = half the window height.