How to measure a window for curtains
Measure the glass or the frame across the top, the middle and the bottom. On an older window these may differ, so use the widest. Then measure the height of the window, and how far the sill sits above the floor, as that decides how long a floor length panel has to be.
The rod runs past the glass, and how far is your first choice. Bali's guide says at least 4 inches a side. That still leaves the curtains over some of the glass when you open them. To clear it, Bali says a stack takes about a third of the window's width in total, so a sixth on each side. Drapery Rods Direct's example adds 30 inches to an 84 inch window, which is near that.
Fullness is then a matter of taste. It multiplies the rod and not the window, as Drapery Rods Direct and this calculator both work it. Some other calculators multiply the window, which gives you less fabric. Linen Chest describes 1.5 times as tailored, 2 times as balanced and standard, 2.5 times as luxurious and 3 times as the most volume. We could find only makers and retailers on this, with no standard behind them.
A worked example
Here is a 60 by 48 inch window with its sill 36 inches up, floor length curtains at 2 times fullness and 54 inch panels. These lines come from the same formula the calculator above runs.
60 by 48 in window, 2 times fullness
- 60 + 8 = 68 in of rod
- 68 × 2 = 136 in of fabric
- 136 ÷ 54 = 2.52, so 3 panels
- 4 + 48 + 36 − 0.5 = 87.5 in long
To clear the glass when open, the rod goes 10 inches past each side, and is 80 inches long. That takes 3 panels at the same fullness. Replacing the window too? The window cost calculator prices that, and the caulk calculator counts the tubes for sealing around it.
Curtains by window width
These use the shortest rod and 54 inch panels at 2 times fullness. The last column is how far past the glass the rod would need to go for open curtains to clear it.
| Window | Shortest rod | Fabric | 54 in panels | Past the glass to clear it |
|---|---|---|---|---|
| 36 in | 44 in | 88 in | 2 | 6 in |
| 48 in | 56 in | 112 in | 3 | 8 in |
| 60 in | 68 in | 136 in | 3 | 10 in |
| 72 in | 80 in | 160 in | 3 | 12 in |
| 96 in | 104 in | 208 in | 4 | 16 in |
| 120 in | 128 in | 256 in | 5 | 20 in |
Mistakes when ordering curtains
- Measuring only the glass. Fullness goes on the rod, so a wider rod means more fabric.
- One panel or a pair. A labeled width may be for either one, so read it carefully.
- No room for the stack. Curtains ordered at the window's width cover part of the glass even when open.
- Forgetting returns and overlap. A workroom adds them on made-to-measure curtains, as Drapery Rods Direct says, and this calculator does not.
- Heavy fabric on a bare minimum rod. Bali says heavy or bulky fabrics may need additional width.
Questions
How wide should curtains be compared to the window?
About twice the rod's width in total, and the rod should be wider than the window. Linen Chest calls 2 times fullness balanced and standard. Bali's minimum rod is the glass plus 8 inches. Fullness is a taste, so this is guidance and not a rule.
How wide should curtains be for a 60 inch window?
About 136 inches of fabric in total, on a 68 inch rod at 2 times fullness. That takes 3 panels at 54 inches wide, since 2 panels only come to 108. If you want them to clear the glass when open, the rod needs to be longer.
How wide should curtains be for a 72 inch window?
About 160 inches of fabric in total, on an 80 inch rod at 2 times fullness. Three panels at 54 inches wide come to 162, which only just covers it. Choose 4 panels if you plan a longer rod to clear the glass.
How many curtain panels do I need?
Multiply the rod by the fullness, divide by your panel's width and round up. Check whether the label's width is for one panel or for a pair, as a common mistake is to treat one as the other. We show both counts.
Where should curtains end?
Wherever suits the room, as we found no standard to cite. The usual choices are the sill, just below it, just above the floor or pooling on it. The figures we use for these are our own starting points, so hold a tape up first.
How wide should curtains be for a sliding glass door?
Work from the rod, as with a window, and leave room for the stack so the door can be used. Bali says the stack takes about a third of the opening's width in total, and heavy fabric takes more. A 72 inch door would add 24 inches.
This curtain estimate rests on maker and retailer guidance, not a standard, and fullness is a matter of taste. Panels differ, so go by the width and length on the label or the supplier's specification, and check whether that width is for one panel or a pair. Old windows can be out of square, and heavy fabric needs more room to gather.
Sources and review
- Measuring guide for drapery hardware, Bali, no date shown, read November 2026.
- Pinch pleat drapery, Drapery Rods Direct, no date shown, read November 2026.
- Understanding curtain fullness, Linen Chest, no date shown, read November 2026.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Rod
Rod = Window + Extension on both sides
- Extension
- At least 4 inches a side, by Bali
Worked through: 60 + 8 = 68 in
Panels
Panels = Rod × Fullness ÷ Panel width, rounded up
- Fullness
- How many times the rod's width the fabric runs
Worked through: 68 × 2 ÷ 54 = 2.52
The constants, and where they come from
MINIMUM_EXTENSION_INCHES
Published range, narrowedLeast a rod should run past the glass per side, in inches
Applies to: One hardware maker's guide, not a standard
Source: Measuring guide for drapery hardware, Bali, no date on the page, read 2026-11.
Bali's guide gives glass width plus 8 inches as the minimum, or 4 inches a side. We found no university or trade body source for this.
STACK_BACK_SHARE
Published range, narrowedRod to add past the glass so open panels clear it, as a share of window width
Applies to: A general rule. Heavy or bulky fabric takes more
Source: Measuring guide for drapery hardware, Bali, no date on the page, read 2026-11.
Also from: Pinch pleat drapery, Drapery Rods Direct, no date on the page, read 2026-11.
Bali says about a third of the window in total. Drapery Rods Direct adds 30 inches on an 84 inch window, where a third would be 28.
DEFAULT_FULLNESS
Published range, narrowedStarting fabric width as a multiple of the rod
Applies to: Retail guidance from a Canadian retailer, and a question of taste
Source: Understanding curtain fullness, Linen Chest, no date on the page, read 2026-11.
Also from: Pinch pleat drapery, Drapery Rods Direct, no date on the page, read 2026-11.
Linen Chest calls 2x balanced and standard, with 1.5x tailored and 3x the fullest. Drapery Rods Direct makes its pinch pleats at 2.5 to 1.
BELOW_SILL_INCHES
ModelledLength past the sill for a below sill curtain, in inches
Applies to: Our own starting point, which you can read as a matter of taste
No published figure exists for this. It is derived, and the derivation is below rather than a citation to something that does not say it. Last checked in November 2026.
We found no readable source on where curtains should end, so this is a design convention and is not a measured figure.
FLOOR_CLEARANCE_INCHES
ModelledGap left above the floor for a floor length curtain, in inches
Applies to: Our own starting point, which you can read as a matter of taste
No published figure exists for this. It is derived, and the derivation is below rather than a citation to something that does not say it. Last checked in November 2026.
We found no readable source on floor clearance, so this small gap is our own convention. Uneven floors may call for more.
PUDDLE_INCHES
ModelledFabric allowed to rest on the floor for a puddled curtain, in inches
Applies to: Our own starting point, which you can read as a matter of taste
No published figure exists for this. It is derived, and the derivation is below rather than a citation to something that does not say it. Last checked in November 2026.
We found no readable source on how much a curtain should puddle, so this is our own convention and you may want more or less.
What the labels mean
- Published range, narrowed:
- a source publishes a range and this calculator uses a representative value from it.
- Modelled:
- derived rather than measured, and the derivation is shown.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the curtain width calculator
- 1
Measure the window's width in several places
- 2
Measure its height and the sill above the floor
- 3
Decide how far the rod runs past the glass
- 4
Choose a fullness
- 5
Read your panel's width from the label
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- Fabric is measured against the rod, not the window
- The rod runs at least 4 inches past the glass on each side
- Length styles are our own starting points, as no source we could read sets them
- No allowance for returns or overlap, which a workroom adds
Pro tips
- Measure an old window's width in several places
- Allow extra stack for a heavy fabric
- Hang the rod before you order the length