Curtain Size Calculator – Find the Perfect Fit
Curtains can make a room feel warm, tall, and finished — or they can look like they were borrowed from a smaller window.
Curtain Size Calculator
Panel width is rounded up to the nearest whole inch. Length allows extra for the heading: rod pocket adds 8 inches, grommet adds 4 inches.
The difference is almost always the size. Too narrow, and they look stretched flat. Too short, and they look like they shrank in the wash.
The trick is simple once you know it: curtains need extra width to gather and fall in soft folds, and the length depends on how they hang.
This free curtain size calculator takes your window measurements and tells you exactly what panel width and length to buy, including the nearest standard length off the shelf.
How to Use This Calculator
EXAMPLE
Let us work through a real window. Your window is 60 inches wide and 84 inches high.
You choose 2x fullness, grommet style, and 2 panels.
First the width: 60 × 2 = 120 inches of fabric in total, divided by 2 panels = 60 inches per panel.
Then the length: grommet curtains add 4 inches to the window height, so 84 + 4 = 88 inches needed.
The standard lengths in shops are 63, 84, 96, and 108 inches.
The nearest standard length at or above 88 inches is 96 inches — so you would buy two panels, each 60 inches wide and 96 inches long, and hem or hang them to sit just right.
If your needed length had been over 108 inches, the calculator would tell you a custom length is needed instead.
THE BOTTOM LINE
Good curtains are really just good measurements with a little extra built in.
The extra width is what gives you those soft, generous folds instead of a flat sheet of fabric, and the extra length is what keeps the hem from floating awkwardly above the floor.
Measure carefully, choose the fullness that suits your room, and buy the standard length the calculator recommends — it is always the next size up, never the one that falls short.
Get the size right once, and your curtains will hang beautifully for years.
Get it wrong, and no amount of styling will quite fix it, so take the two minutes to measure and calculate before you shop.
Frequently Asked Questions
What is fullness, and why does it matter?
Fullness is how much extra fabric you buy beyond the width of the window. A curtain as wide as the window hangs flat and stretched. At 2x fullness, the curtain gathers into soft folds.
Should curtains touch the floor?
For most living rooms and bedrooms, yes — curtains look best when they just kiss the floor or hover a finger-width above it. That is why the calculator adds length for the heading rather than stopping at the window height.
What is the difference between rod pocket and grommet curtains?
Rod pocket curtains have a sewn pocket at the top that the rod slides through, so they need 8 inches of extra length. Grommet curtains hang from metal rings, so they need just 4 inches of extra length.
Why does the calculator round the panel width up?
Fabric is sold by the inch, and a panel that is half an inch too narrow will look stretched when closed. Rounding up to the nearest whole inch makes sure you always have enough fabric for the fullness you chose.
What if my window needs a length above 108 inches?
Then a standard off-the-shelf length will fall short, and the calculator will say a custom length is needed. Very tall windows, floor-to-ceiling windows, and rooms with high ceilings often need this.
Should I measure the window or the curtain rod?
Measure the window for this calculator, and hang your rod a few inches wider than the window on each side. A wider rod lets the curtains stack off the glass when open, so more light comes in.
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