Curtain Calculator

How many panels, how wide a rod, and how high to hang it.

Window width (in)

Outside edge of the casing, side to side

Curtain style

Panel width (in)

Most ready-made panels are 50″

Hanging height (optional)

Floor to top of window (in)

Ceiling height (in)

Where to hang the rod

Curtains make a window look bigger or smaller depending almost entirely on where you put the rod. This works out the rod width, the height, and how many panels you need to look full rather than skimpy.

How it works

The rod should extend 4 to 8 inches past the window frame on each side, so that the open curtains stack beside the glass rather than covering it. It hangs high — typically 4 to 6 inches above the frame, or close to the ceiling for a taller look. Panel count comes from fullness: the combined width of the panels should be about twice the width of the rod for a proper gathered look.

Example

A 36-inch-wide window with the rod extended 6 inches each side gives a 48-inch rod. For 2× fullness you need about 96 inches of curtain — two standard 50-inch panels.

Tips & common mistakes

Hang the rod high and wide. High and wide is the entire trick: it makes the window look far larger and the ceiling far taller, and it costs nothing.
Two panels are the minimum for almost any window. A single panel pulled across looks flat and thin, no matter how nice the fabric is.
Curtains should just touch the floor, or break slightly on it. Curtains that stop short of the floor are the fastest way to make a room look unfinished.
Measure from where the rod will actually go — not from the top of the window frame — or your panels will be several inches too short.

Frequently asked questions

How high should you hang curtains?

4 to 6 inches above the window frame at a minimum, and closer to the ceiling if you want the room to feel taller. Hanging the rod right on the frame is the most common mistake.

How wide should a curtain rod be?

The window width plus 8 to 16 inches, so the rod extends 4 to 8 inches past each side. That lets the open panels sit beside the window rather than blocking the light.

How many curtain panels do I need?

Enough that the panels together are about twice the rod width. For most windows that means two panels; for wide windows, four.