What Is the Curtain Size Calculator?
This tool helps you work out exactly how wide and how long your curtains should be so they hang beautifully and fully cover your window. It combines your window measurements with a fullness ratio (how gathered the fabric looks) plus practical sewing allowances for the header and hem. The calculator works in centimetres and applies to any standard window or curtain rod.
How to Use It
Measure the width of your window or curtain rod and enter it. Choose a fullness ratio — typically 1.5 for a light gather, 2.0 for a standard look, and 2.5–3.0 for a luxurious, full pleat. Enter the distance from the rod to the floor (or sill), then add your header allowance (the fabric folded over the top, often 8–15 cm) and hem allowance (the bottom turn-up, often 10–20 cm). Finally enter how many panels you want; the calculator divides the total width across them.
The Formula Explained
Total curtain width = window width × fullness ratio. A 120 cm window at a fullness of 2 needs 240 cm of fabric width so the curtain still looks full when drawn closed.
$$\text{Width per Panel} = \frac{\text{Window Width} \times \text{Fullness Ratio}}{\text{Panels}}$$Curtain length = rod-to-floor + header + hem. Adding these allowances ensures you have enough fabric to sew the top channel and bottom hem without losing your finished drop.
$$\text{Curtain Length} = \text{Rod to Floor} + \text{Header} + \text{Hem}$$
Worked Example
For a 120 cm window with fullness 2, rod-to-floor of 230 cm, a 10 cm header and 15 cm hem across 2 panels: width = \(120 \times 2 = 240\) cm, length = \(230 + 10 + 15 = 255\) cm, and each panel needs \(240 \div 2 = 120\) cm of width.
FAQ
What fullness ratio should I choose? 1.5 is economical, 2.0 is the most popular balanced choice, and 2.5–3.0 gives a rich, heavily gathered look ideal for formal rooms.
Should curtains touch the floor? For a clean look use rod-to-floor exactly; for a puddled or break style, add 5–20 cm to the rod-to-floor measurement before entering it.
Does this include side returns? No — if you want fabric to wrap to the wall, add a few extra centimetres to your window width before calculating.
