Free Curtain Size calculator
Enter your window width, fullness, panel width, and the drop to your endpoint to get the total curtain fabric width, the number of panels to buy, and the finished length — updated live, as you type.
On this page14 sections
Estimates only, based on the measurements you enter. Confirm panel sizes with the retailer.
Results are estimates. Consult a professional.
How the curtain size calculator works
Curtains look full because the fabric is wider than the window it covers. The calculator takes the width you want to cover, multiplies it by a fullness ratio to get the total fabric width, then divides that by the width of one ready-made panel to tell you how many panels to buy. Separately, it takes your finished-length measurement — the drop from the rod down to your chosen endpoint — and reports it as the panel length to order.
What the result tells you
Three numbers do the work. The total fabric width is how much curtain has to span the window for the look you chose. The panel count is what you buy off the shelf, rounded up so the window is never under-covered. The recommended length is the finished drop — the height the panels need to be, hemmed and hung, to reach the floor, sill, or puddle you picked.
What goes into your curtain measurements
A curtain order is built from three measurements. Get each one right and the panels hang full and reach the floor; miss one and the curtains look skimpy, sit too short, or leave gaps at the sides.
Coverage width — measure the rod, not the glass
This is the width the fabric has to span. Measure the rod, not just the window, because the rod should run 3–6 in past each side so open curtains clear the glass and let light in. A 60-inch window with a rod extended 6 in each way has a 72-inch coverage width — and that larger number is what fullness multiplies.
Fullness ratio — how much extra fabric makes the gathers
Fullness is the ratio of fabric width to coverage width, and it is the single biggest lever on how the curtains look. At 1.5× the panels look flat and tailored; at 2× they gather into the standard, most-popular fold; at 2.5× they read full and luxurious. Sheers want more, not less, because thin fabric needs extra width to look like anything at all.
Finished length — the drop to your endpoint
Length is a straight measurement from where the rod sits down to where you want the panels to stop. Build it from three pieces: how far above the window you mount the rod, the window's own height, and the distance from the sill down to your endpoint. The calculator returns that drop unchanged — add a hem and header allowance only if you are buying yardage to sew.
A worked example using the curtain size calculator
Maya is dressing a 60-inch living-room window. She'll mount the rod 6 in above the frame and extend it 6 in past each side, wants the standard 2× gathered look, and is buying 50-inch ready-made panels to reach the floor.
Step 1 — Find the coverage width
The rod runs 6 in past each side of the 60-inch window: 60 + 6 + 6 = 72 in of coverage width. That is the number fullness multiplies, not the bare 60-inch glass.
Step 2 — Multiply by fullness for total fabric width
At the standard 2× fullness, 72 × 2.0 = 144 in of total fabric width. That is how much curtain has to span the window to gather properly.
Step 3 — Divide by panel width for the panel count
Each panel is 50 in wide, so 144 ÷ 50 = 2.88, rounded up to 3 panels. You can't buy 2.88 panels, and three guarantees the window is never under-covered.
Step 4 — Build the finished length
Rod 6 in above the frame + the 60 in window height + 12 in from sill to floor = a 78 in drop. Maya orders 84-inch panels (the next stock length) and has them hemmed to 78 in.
How wide should curtains be? Fullness ratios explained
The short answer: wider than the window. The standard rule is to make the total fabric 2 to 2.5 times the width you're covering, dialing it down to 1.5× for a tailored look or up to 3× for a dramatic, heavily gathered one. Pick the ratio first, because it sets both the total fabric width and the panel count.
| Fullness ratio | Look | Best for |
|---|---|---|
| 1.5× | Tailored, light gathers | Grommet and rod-pocket panels, casual rooms |
| 2.0× | Standard gathered (most popular) | Most living rooms and bedrooms |
| 2.5× | Full and drapey | Pleated drapes, formal spaces, sheers |
| 3.0× | Dramatic, very full | Statement windows, theatrical fullness |
Fullness is fabric width ÷ coverage width. Sheers and lightweight fabrics need the higher end of the range to look full and provide privacy.
One common mistake is applying fullness to the window glass instead of the rod. The rod is wider, so the fabric should be too — measure the rod width, multiply by your ratio, and the gathers come out right.
Standard curtain lengths: sill, apron, floor, and puddle
Length is where curtains most often go wrong — too short reads cheap, too long drags. Your endpoint sets the drop. This table gives the four standard stopping points and how each is measured from the rod down.
| Length | Where it stops | How to measure the drop |
|---|---|---|
| Sill | At the windowsill | Rod to the sill — common in kitchens and bathrooms |
| Apron (below sill) | A few inches below the sill | Rod to about 4 in below the sill, for a neat finish |
| Floor | Just clearing the floor | Rod to ½ in above the floor — the tailored, formal look |
| Puddle | Pooling on the floor | Rod to floor, then add 6–8 in of extra fabric |
Floor-length and puddle are the most popular for living rooms and bedrooms. Sill and apron suit windows over counters, radiators, or furniture.
Ready-made panels come in stock lengths — 63, 84, 95, and 108 in are typical. Buy the next length above your drop and hem the rest, or pick a rod-pocket style that adjusts a little.
How many curtain panels do I need?
This is the question most curtain calculators skip, and it's the one that decides what you put in the cart. Take your total fabric width, divide by the width of one panel, and round up. The rounding matters: a fractional panel can't be bought, and rounding down leaves the window under-covered.
The formula
Panels = round up( coverage width × fullness ÷ panel width ). For the worked example: 72 × 2.0 = 144 in of fabric, divided by a 50-inch panel = 2.88, rounded up to 3 panels.
Round up to an even number for pairs
Curtains hang best in symmetric pairs, one stack on each side. So once the math gives you a minimum, round up to the next even number: a 3-panel result usually becomes 4 (two per side). It costs one more panel but buys symmetry and a little extra fullness — the look most people are after.
How to measure your window for curtains
Good curtains start with three measurements taken in the order you'll hang them: rod position, then width, then drop. Use a steel tape, measure each window separately, and write the numbers down — eyeballing is how panels end up short.
- Set the rod position first. Decide how high above the frame the rod goes (4–6 in is standard, higher for taller-looking ceilings) and how far past each side (3–6 in). This fixes both your width and your drop.
- Measure the coverage width. Measure end to end across the rod, including the extension past both sides. This is the number you multiply by fullness — not the window opening.
- Measure the drop to your endpoint. From the rod down to the sill, below-sill, floor, or puddle line. Measure to where the rings or rod pocket will sit, not the top of the bracket.
- Pick a fullness ratio. 1.5× tailored, 2× standard, 2.5× full. Plug all three numbers in and the calculator returns your total fabric width, panel count, and length.
For sewn or custom drapes, add a hem and header allowance — often 8 in or more — on top of the finished drop. Ready-made panels already include their hems, so order to the next stock length above your measured drop.
Curtain sizing definitions
How accurate is this curtain size calculator?
The width and panel math is exact. Coverage width times fullness is the precise total fabric width, and dividing by panel width and rounding up is the exact panel count for the look you chose. If your rod measurements are right, those numbers are right.
The length is only as good as your endpoint measurement, so measure the drop with the rod in its final position. Two judgment calls stay with you: fullness is a style choice within the 1.5–3× range, and whether to round the panel count up to an even pair is up to your eye and budget. Ready-made panel widths and stock lengths vary by brand, so confirm the size on the listing before you order. For custom-sewn drapes, add your hem and header allowance on top of the finished drop — the calculator reports the visible length, not the cut-fabric length.
Frequently asked questions about the free Curtain Size calculator
About this Curtain Size calculator
This curtain size calculator runs entirely in your browser — nothing you enter is sent anywhere, and the total fabric width, panel count, and recommended length update the moment you change a measurement.
It pairs the standard drapery fullness rule with a real panel-count step, so you know exactly what to put in the cart. Browse more home projects in Home & Garden, or see the full set of free tools on the calculators index.