How to measure for curtains

Last reviewed October 21, 2026

Curtains need two measurements from your home, the rod span and the drop, and two facts from the product listing, the width basis and the length. Take them in this order and the math becomes simple.

What you need

• A steel tape measure. Cloth tapes stretch.
• Paper or your phone's notes, one line per window. Windows that look the same are often a little different.
• The product listing you are considering, if you have one.

1. Rod span (width)

If the rod is already up

Measure the length of rod the curtains can slide along: between the brackets, or between the end caps if the curtains can slide past the brackets. If the rod has a support bracket in the middle, curtains usually cannot pass it, so measure each side separately.

If you are choosing a rod

Measure the window from one outer edge of the frame to the other. IKEA's guide suggests adding at least 6 in on each side, so the curtains can be pulled clear of the glass when open. For the example window, 64 + 6 + 6 = 76 in.

2. Drop (length)

Pick a reference point you can measure from, ideally the top of the rod, and measure straight down to where the curtains should end. IKEA's guide measures from the top of the window frame and adds space above it for the rod: in the example the frame top is 80 in above the floor and the rod top 6 in higher, at 86 in. With the hems just clearing the floor the drop is 85.5 in. How the curtain top sits on the rod changes the length to buy; the curtain length guide shows how.

3. Read the listing

1. Width basis: is the width for one panel or the whole pack? See per panel or per pair.
2. Panels per pack: 1 for a single panel, 2 for a pair or set of 2.
3. Length: the length printed on the listing, and how the top is made (grommets, rod pocket, tabs, or a plain top for rings or hooks).

4. Inches or centimeters

Use one unit for everything. Fractions from a US tape are fine: 76 1/2 in is 76.5 in. To convert, 1 in = 2.54 cm exactly, so 76 in is 193.04 cm. The calculators accept either unit and convert without rounding the result.

Put it together

For the example window, the 76 in rod span with example listing A from the width guide (52 in panels, 2 per pack) at fullness 2, opening in the middle, gives 4 panels to hang and 2 packs to buy. Enter your own numbers in the Curtain Panel Calculator.