Most orders default to two panels per window, whether the window is 24 inches wide or 96. That is why some rooms end up with curtains that read flat, and others end up with fabric puddled at the sides and a rod that sags. The right number falls out of a single formula: (window width × 2) ÷ panel width, rounded up. Never rounded down.
The formula is easy. The tricky word is “width”, because there are three of them in play, and each one gets measured differently. Rod width, panel width, and window width are not the same number, and mixing them up is how most rooms end up under or over-filled. This calculator is one chapter of our complete curtain install hub.
🧮 The Panel Calculator
Window / rod width
W inches
Fullness
2
Panel width
P inches
Panels
N ↑
Round up, never down. A 2.4 result becomes 3 panels, not 2.
One panel that replaces two
Liz Linen Extra Wide Curtains Pleated
from $59.99/panel · 10% linen / 90% polyester · 350 gsm · 112 inches wide · pinch pleat · 6 warm colors. Final price depends on size and lining.
Use code JULY for 20% off · Free shipping over $300
The 2x Fullness Rule (Why Two Panels Are Not Always Right)
Every number in this article comes back to one line: a curtain drapes properly when the flat fabric it is cut from is twice as wide as the rod it hangs on. Publications like the The Spruce sizing reference repeat the same 2x rule for a mechanical reason: below 2x, the panel has nothing to fold into.
At 1.5x fullness the closed curtain reads flat, with shallow pleats and daylight leaking between them. At 2x the fabric has room to form the S-curve that catches light along the edges. At 2.5x or 3x, which velvet and heavyweight linen support, the drape starts reading custom.
📊 What fullness actually looks like
1.5×
Flat, sheer only
Reads like a bedsheet on opaque fabric. Acceptable for lightweight sheers meant to lie almost flat.
2×
Standard drape
The floor for opaque cotton, linen, and blends. Pinch pleat and grommet look intentional at this ratio.
2.5×
Luxury linen
Heavyweight linen at 300 to 400 gsm holds its shape at this fullness, with deeper pleats and a softer face.
3×
Custom velvet
Velvet, dupioni silk, and blackout linen at 3x fullness read hotel-suite. Expensive, high panel count.
Ratio choice is not aesthetic freedom, it is fabric physics. A sheer at 3x pools and looks accidental. A velvet at 1.5x looks rented from a college theatre.
⚠️ Warning
1.5x is not fullness, it is a bedsheet. The most common way people miss the number is by measuring the window (not the rod), multiplying by only 1.5, and calling it done. On any opaque fabric, that gives you a curtain that hangs flat and lets light through the pleats.
Step 1: Measure the Right Width to Start From
The single biggest mistake in the calculation is multiplying the window width by two. A window is 36 inches, but the rod that carries the curtain almost never is. Designers work from the rod width, which usually adds 6 to 12 inches of stack-back on each side of the frame, so the open panels park on the wall instead of covering glass.
The concrete formula: window frame width + 12 to 24 inches of total stack-back = rod width. That rod width is the number you multiply by two. A 36 inch window with a 6 inch stack per side becomes a 48 inch rod, which at 2x fullness needs 96 inches of panel.
How High To Hang Curtains: The Designer Rules for Every Ceiling
Panel count depends on rod width, and rod width depends on rod height. Fix the height first so the width you feed the calculator is the right one.
Tip 📏: measure the rod, never the window. If the rod is not up yet, decide the height first, mark both bracket points on the wall, and measure that line. The two-inch gap you leave on either side of the frame changes the whole panel count.
| Window width | Rod width (approx) | Total panel width at 2× | Standard 50″ panels | Two Pages 112″ Extra Wide |
|---|---|---|---|---|
| 24″ | 36″ | 72″ | 2 panels | 1 panel (single draw) |
| 36″ | 48″ | 96″ | 2 panels | 1 panel (single draw) or 2 for pair |
| 48″ | 60″ | 120″ | 3 panels | 2 panels (pair) |
| 60″ | 72″ | 144″ | 3 panels | 2 panels (pair) |
| 72″ (sliding door) | 84″ | 168″ | 4 panels | 2 panels (pair) |
| 96″ (large bay) | 108″ | 216″ | 5 panels | 2 panels + filler or 3 pair |
| 120″ (wide slider) | 132″ | 264″ | 6 panels | 3 panels |
Step 2: Divide by Your Panel Width (And This Is Where Retail Fails)
The stocked 50 inch panel exists because trucks and warehouses like round pallets, not because 50 inches makes sense for how windows are actually built. Two Pages custom-width panels run 50 to 84 inches per panel depending on the collection, and the Two Pages Extra Wide line hits 112 inches per panel, effectively doubling the retail default in a single unit.
📐 Panel widths on the market
50 to 54″
Ready-made retail
The pallet-friendly size. Covers a single 24 to 27 inch window at 2x. Anything wider drives your panel count up fast.
50 to 84″
Two Pages custom width
Standard Two Pages made-to-order collections. Match the panel width to the window, no filler seams.
112″
Two Pages Extra Wide
The single-panel answer to wide windows. One panel does what two stocked retails try to.
Worked example: a 60 inch window with a 12 inch stack-back gives a 72 inch rod. At 2x that is 144 inches of panel width required. Divided by 50 gives 2.88 panels, which rounds up to 3 stocked panels of 50 inches. Divided by 112 gives 1.29 panels, which rounds up to 2 Extra Wide panels for a proper symmetric pair.
⚠️ Warning
Never round down. Rounding 2.88 down to 2 gives you a 1.39x fullness curtain that reads flat, exactly the outcome the 2x rule exists to prevent. Rounding up costs one extra panel and preserves the drape.
When One Panel Works and When It Does Not
The Architectural Digest hanging guide lists three scenarios where a single panel reads intentional: a sliding glass door with a single-side draw for daily traffic, a narrow window under 30 inches wide where a pair would collide in the middle, and a decorative sheer accent layered over another treatment.
Outside those cases, a lone panel on a 36 to 48 inch bedroom window looks off-balance in both positions: half the glass exposed when open, half unnaturally curved when closed. That is the effect people describe as “bathroom curtain” because it is what stall dividers do.
🪟 Where one panel is the right answer
Sliding glass door, single draw
One 112 inch Extra Wide covers a 72 inch door, stacks to one side, and clears the walkway for daily access.
Narrow window under 30″
A pair would meet on top of the glass. One panel, drawn to one side, respects the proportion.
Sheer over a solid drape
The sheer is decorative, not functional. A single panel adds softness without a second count.
⚠️ Warning
One panel on a bedroom window creates a bathroom effect: half open, half covered, always uneven. If the window sits between 30 and 60 inches wide and lives in a bedroom, dining room, or living room, order the pair.
When One Extra Wide Panel Replaces Two Standards
The Two Pages Extra Wide line, sourced from the Liz Extra Wide product page, is cut at 112 inches, which is roughly the width of two stocked 50 inch panels sewn together, minus the seam.
Standing at a 96-inch bay window with a bag of retail panels is how most rooms end up flat. A 48 inch window with a 12 inch stack-back becomes a 60 inch rod, which at 2x needs 120 inches of panel. That is one 112 inch Extra Wide plus 8 inches of overlap on the opposite side, or two Extra Wide panels for full drape and a clean symmetric pair.
Two Pages Liz Linen Extra Wide Curtains Pleated: The Full Review
The 112 inch panel that changes the math for wide windows: drape test, dye lot behavior, verdict on which colorways ship most consistently.
Read Review →
If it were my dining room, one Extra Wide behind each side of the trim, no second panel, no seam down the middle. The hidden win: one panel per side means one dye lot per side. Two 50 inch panels ordered together can still shift a shade off each other after a dozen wash cycles. A single 112 inch Liz Extra Wide panel removes that risk.
📊 Extra Wide vs two standards
Two 50″ stocked panels per side
• One seam between panels, visible when closed
• Two dye lots to match at order time
• Two rod pocket or clip sets to feed
• 100 inches total width per side at $30 to $60 stocked prices
One 112″ Liz Extra Wide per side
• Zero seams, uninterrupted drape
• One dye lot per side, no color mismatch
• One pinch pleat header per side
• 112 inches per panel at from $59.99, heavyweight 350 gsm linen blend
112 Inches Wide Cuts Your Panel Count in Half
A 72 inch window at 2x fullness needs 144 inches of panel width. That is three 50 inch stocked panels, or one Liz Extra Wide plus a filler, or the cleanest answer: two Liz Extra Wide panels for full luxury drape at from $59.99 each.
Layering Sheers and Blackouts Doubles the Count
A double rod carries two layers, and each layer is its own calculation. The sheer in front and the drape behind get counted separately, at whatever fullness fits each fabric.
Sheers at 1.5x fullness are acceptable because the fabric is meant to hang lightly. Drapes behind them stay at 2x minimum, and if the drape is heavyweight linen blend like the Kyla or Liz collections, 2.5x reads even better. For ceiling-to-floor layers on a wall of glass, the full Kyla Extra Long ceiling to floor review covers the drop math that pairs with this width math.
🎨 Layering counts, layer by layer
Layer 1: Sheer in front
1.5x fullness acceptable. Stocked sheer panels at 50 to 54 inches are usually enough for windows up to 45 inches wide.
Layer 2: Drape behind
2x fullness minimum for opaque fabric. Custom width recommended once the window goes past 48 inches so the drape does not read flat.
Alternative: Blackout lining
Two Pages adds a blackout lining inside the drape itself. One rod, one count, one purchase. Cheaper than a separate blackout panel and simpler to hang.
The third option is not a layer at all. Two Pages custom drapes can be ordered with a built-in blackout lining, which turns two panels into one product and keeps the count where it was.
Pro Tips Before You Add to Cart
Tip 📏: order every panel for a single window in one transaction, on one order line. Two Pages ties dye lot to the order, and splitting an order across two carts is how symmetric pairs end up one shade off. Handcraft tolerance on drops is roughly one inch per panel, so if you need identical lengths, all panels have to come from the same lot.
Tip 📏: run a tape mock before ordering. Cut a strip of newspaper or a bedsheet to the panel width you are considering, tape it to the wall where the rod will sit, and step back. It reveals whether one 112 inch Extra Wide looks like too much fabric or exactly enough, in the actual light of the actual room.
Two Pages In-Home Measurement & Installation Service
Big bay, corner window, or a rod that curves? Two Pages sends a measurer, orders the exact panel count, and installs. Real cost and eligibility, reviewed.
Tip 📏: when the calculator gives you a half panel, round up. Never down. If the price of the extra panel is the sticking point, use the Two Pages zoom measuring consultation to double-check whether a wider single panel option (Extra Wide, custom width) can carry the room at your budget instead.
🧵 Three tips worth writing down
1. Same order, same dye lot
Order every panel for a single window on one order line. Splitting risks a two-shade mismatch on the same rod.
2. Tape a full-width mock
Newspaper or bedsheet at the actual rod height reveals whether the panel width you picked reads full or fussy in the real room.
3. Add 6 inches for the stack
Push the rod 6 inches past each side of the trim so open panels park on wall, not glass. That extension changes your panel count.
See the Fullness Before You Order the Count
Even a two-shade difference between panels reads as a dye lot mismatch on the same rod. The 38-color Liz Blend Booklet ships flat for $3.99 so you can compare your finalists at your actual window before deciding on one panel, two, or three.
Once the count is set and the rod width is fixed, the last thing left is choosing which of those panels ships in a width that matches yours cleanly. That is where retail loses and custom wins.
You Know the Count. Order the Width That Matches.
Multiply your window width by two, divide by 112, and Liz Extra Wide ships that many panels at the exact drop you need. from $59.99/panel, 350 gsm, 6 warm colors, sold individually so you can order odd counts. Code JULY (20% off) · Free shipping over $300.
Frequently Asked Questions
How do I calculate how many curtain panels I need?
Use one formula: (window width × 2) ÷ panel width, rounded up. Multiply your rod width, not your window width, by two for the 2x fullness that makes curtains drape instead of hang flat. Divide by the width of a single panel you plan to buy: 50 inches for stocked retail, up to 112 inches for Two Pages Extra Wide, or a custom cut per panel for made-to-order. Always round up. A 72-inch rod at 2x fullness needs 144 inches of panel, which is three 50-inch panels or two Extra Wide.
Do I need one or two curtain panels per window?
Two panels are the default for a symmetric pair look, one on each side of the window, which is what most living rooms and bedrooms want. Use one panel only when the design calls for a single-side draw: sliding glass doors, narrow kitchen windows under 30 inches, or a decorative accent over a sheer. A single panel on a standard 36 to 48 inch bedroom window looks off-balance in both open and closed positions.
How wide should each curtain panel be?
Each panel should cover at least the full width of the window it flanks plus stack-back space. For a symmetric pair, each panel needs to be at least the window width, so that when they meet in the middle you have 2x fullness. Standard retail panels ship at 50 inches, which is fine for windows up to about 45 inches wide. For a 60 inch or wider window, standard panels get stretched too thin: choose custom-width or 112 inch Extra Wide.
How many curtain panels do I need for a sliding glass door?
A standard 6-foot sliding glass door is 72 inches wide, so 2x fullness needs 144 inches of panel. That is three 50-inch stocked panels, two 84-inch custom panels, or two 112-inch Extra Wide for a luxury drape with only one dye lot per side. If the design calls for a single-side draw for daily access, one Extra Wide panel of 112 inches covers a 72-inch door at 1.55x fullness, which reads flatter but functions.
How many curtain panels do I need for a bay window?
Measure each flat section of the bay separately, apply 2x fullness to each, and add the counts. A three-section bay of 30 + 48 + 30 inches (108 inches total) at 2x needs 216 inches of panel: five 50-inch panels or two Extra Wide plus a filler. Angled corners often benefit from a single continuous rod system with panels flanking the outer edges only, so recount after choosing the rod path.
Can I use just one curtain panel on a window?
Yes, for single-side draw scenarios: sliding glass doors, narrow kitchen or bathroom windows under 30 inches, closet doorways, or as a decorative sheer accent over another treatment. Avoid a single panel on standard bedroom or living room windows, where it creates an uneven silhouette in both positions. Pinch pleat and grommet headers work best for one-panel draws because they stack cleanly to one side.
What happens if I use only 1.5x fullness instead of 2x?
The curtain reads flat in the closed position, more like a bedsheet than a drape. Pleats fall shallow, light leaks between them, and the room loses the visual softness curtains are supposed to add. 1.5x fullness is acceptable only for sheers, which are supposed to hang lightly. For opaque drapes, stay at 2x minimum; velvet and heavyweight linen blends can go to 2.5x or 3x for a luxury custom look.
