About the Curtain Size Calculator
This curtain size calculator turns a window measurement into everything you need to shop for curtains or drapes: the rod length, the total curtain width for the fullness you want, the finished length for sill, below-sill, floor or puddled curtains, and how many ready-made panels to buy along with the nearest standard length.
It suits anyone buying ready-made panels, ordering custom drapes or sewing their own. The rod usually extends beyond the window frame on each side so open curtains stack against the wall instead of covering the glass, and it is mounted a few inches above the frame (higher makes a window look taller). Fullness is the ratio of flat fabric width to rod length: 1.5× looks tailored, 2× is the standard, and 2.5–3× gives a luxurious, heavily gathered look.
Standard ready-made lengths are 63, 84, 95, 108 and 120 in. Floor-length curtains look best finishing about ½ in above the floor; puddled curtains add 6 in or more. The calculator measures the length from the rod; if your rings or clips add drop, subtract that from the panel length.
With the default inputs, the panels to buy is 4. Change any value above to recalculate instantly.
How to use the curtain size calculator
- 1Measure the window width and height across the outside of the trim.
- 2Measure from the floor to the bottom of the frame.
- 3Decide how far past the frame and how high above it the rod will go.
- 4Pick a length style and fullness.
- 5Read the rod length, panel count and the standard length to buy.
Formula and method
The rod spans the window width plus the extension on each side. Multiplying the rod length by the fullness factor gives the total flat fabric width needed so the curtains still look gathered when closed; dividing by the width of one ready-made panel and rounding up gives the number of panels, rounded up again to an even number for a center-split pair.
Length is measured from the rod: the rod height above the frame plus the window height reaches the bottom of the frame. Sill-length curtains stop ½ in above that, apron-length curtains 4 in below it, floor-length curtains ½ in above the floor (adding the floor-to-frame distance) and puddled curtains 6 in beyond the floor. The nearest standard ready-made length at or above the result is suggested so you can hem it to fit.
- W
- Window width outside the frame
- E
- Rod extension beyond the frame on each side
- F
- Fullness ratio (fabric width ÷ rod length)
- A
- Rod height above the top of the frame
- H
- Window height
- S
- Floor to bottom of the window frame
Worked examples
48 × 60 in window, floor-length pair at 2× fullness
The rod is 48 + 2 × 6 = 60 in. Twice that is 120 in of fabric, which takes 2.4 panels of 50 in — rounded to 3 and then to 4 for an even pair. Length is 4 + 60 + 30 − 0.5 = 93.5 in, so buy 95 in panels and hem 1.5 in.
Kitchen window, sill length, 1.5× fullness
A 36 + 8 = 44 in rod at 1.5× needs 66 in of fabric, so two 42 in panels. Sill length is 3 + 36 − 0.5 = 38.5 in; ready-made panels start at 63 in, so a café or custom length is a better fit.
Wide patio door, puddled single panel at 2.5×
The rod is 72 + 20 = 92 in, and 2.5× fullness needs 230 in of fabric, or 4.26 → 5 panels of 54 in drawn one way. Length is 6 + 80 + 0 + 6 = 92 in, so 95 in panels with a 3 in hem.
Frequently asked questions
How wide should curtains be compared to the window?+
The combined flat width of all panels should be about 2 times the rod length for a standard look, 1.5 times for a tailored look and up to 3 times for sheers. The rod itself should extend 3–12 in beyond the frame on each side.
How long should curtains be?+
Floor-length curtains should end about ½ in above the floor, sill-length about ½ in above the sill and apron-length about 4 in below it. Puddled curtains add 6–8 in onto the floor.
How high should a curtain rod be mounted?+
A common guide is 4–6 in above the window frame, or about two-thirds of the way between the frame and the ceiling. Mounting higher makes the window and room feel taller, but you will need longer panels.
How many curtain panels do I need for a 60 inch window?+
With 6 in extensions the rod is 72 in, so 2× fullness calls for 144 in of fabric — three 50 in panels, rounded up to four for a center-opening pair.
Should curtain length include rings or clips?+
Yes. Panel length is usually measured from the top of the panel, so if rings or clip hooks add 1–2 in of drop below the rod, subtract that from the length shown before buying or hemming.