What fullness ratio should I use?

A ratio of 2.0–2.5 is standard for most curtain styles and gives a good gather. Eyelet curtains typically use 1.5–2.0. Pencil pleat and pinch pleat curtains look best at 2.0–2.5. For sheer fabrics, go up to 3.0 for a luxurious look.

How do I measure curtain drop?

Measure from the curtain rod (or track) down to where you want the curtain to end. For floor-length curtains, subtract 1–2 cm so the curtain just clears the floor. For sill-length, measure to 1 cm below the sill. Add header and hem allowances on top of this measurement.

What is a header allowance?

The header allowance is the extra fabric above the finished drop that forms the top of the curtain — the part that is folded or pleated to attach to the track. A typical pencil-pleat tape needs 8–12 cm; eyelet headers need 4–6 cm to fold behind.

How many panels do I need?

Most windows use 2 panels that meet in the middle. A single panel works for a cafe curtain or a very narrow window. For very wide windows (over 3 m), consider 3 or 4 panels so each one stays manageable and the fabric hangs well.

Should the curtain width be wider than the window?

Yes. For the curtain to stack clear of the glass when open, extend the rod 15–20 cm beyond each side of the window. The calculator adds this as a "track overhang" so your total track width is already wider than the window.

Curtain Size Calculator

Name: Curtain Size Calculator
Availability: InStock
Author: Nham Vu

Enter your window dimensions, header type, and fullness ratio to get the exact curtain panel width and drop you need.

Window & Curtain Details

Units:

Window width (cm)

Window height (cm)

Track overhang each side (cm)

Extra rail beyond each window edge so curtain clears glass when open.

Header style

Fullness ratio

1.5 = light gather · 2.0–2.5 = standard · 3.0 = very full

Number of panels

Header allowance (cm)

Hem allowance (cm)

Fill in the details on the left and click Calculate.

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Summary

Enter your window dimensions, header type, and fullness ratio to get the exact curtain panel width and drop you need.

How it works

Enter the window width and height in either centimeters or inches.
Choose your header type — pencil pleat, eyelet, tab top, or pinch pleat — to set the standard fullness multiplier.
Adjust the fullness ratio if you want a lighter or heavier gather.
Enter how many panels you want (typically 2) and any hem/header allowances.
The calculator shows the cut width and drop per panel, plus total fabric needed.

Use cases

Buy the right curtain size before visiting a fabric store.
Calculate how many meters of fabric to order for custom-made curtains.
Check if ready-made panels are wide enough for your window.
Plan floor-length vs sill-length drops for different rooms.
Size blackout curtains that fully overlap the window frame.
Calculate fabric for multiple windows in a room remodel.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu