Curtain Fabric Calculator
Convert track width, target fullness, usable fabric width, finished length, header and hem allowances, vertical pattern repeat, and contingency into a cutting ticket. The workroom card exposes whole-width drops, actual gross fullness, pattern-match growth, panel distribution, and rounded purchase yards.
Measure the installed opening and fabric
A 60.0 in covered width at 2.00× fullness needs 120.0 in flat. With 54.0 in usable fabric, cut 3 drops. The 98.0 in raw cut rounds to 108.0 in for an 18.0 in vertical repeat. Base yardage is 9.000 yd; 10.0% contingency and one-eighth-yard purchase rounding produce a 10.000 yd plan. Confirm the actual workroom layout before cutting.
How full-width drop planning works
Curtain fullness is the amount of flat fabric relative to the width it covers when installed. A 60-inch span at 2.0× fullness calls for 120 inches of flat finished treatment width. Dividing by 54 inches of usable fabric gives 2.222 widths, which must round up to three full vertical drops for this method.
Whole-width rounding creates 162 inches of gross usable width and a 2.70× gross ratio. That is not automatically the final fullness. A workroom may trim widths, remove selvages, make seams, split a center width between two panels, allocate returns and overlaps, or select a heading that consumes width. The card exposes the excess so it can be designed, not forgotten.
drops = round up(target flat width ÷ usable fabric width)
raw cut length = finished length + top allowance + bottom allowance
matched cut = round up(raw cut ÷ vertical repeat) × vertical repeat
base yards = drops × matched cut inches ÷ 36
Usable width is not bolt width
Measure between the usable edges after deciding how selvages, side seams, joining, lining, and pattern placement will be handled. A fabric sold as 54 inches may not provide 54 flawless, square, pattern-usable inches. Railroaded fabric changes the layout and is not supported by this vertical-drop model.
Utah State University Extension sewing resources note that fabric comes in different widths and emphasize straightening and preparation. Obtain a cutting of the exact fabric, inspect the weave, and verify width, grain, repeat, nap, shrinkage, and care before ordering a large quantity.
Do not cut from calculator output alone
Make a scaled cutting plan showing every drop, seam, panel center, leading edge, return, overlap, header, hem, motif position, lining, interlining, and trim. Check the full shipment for dye lot, flaws, bowing, skew, damage, and repeat variation. Once patterned fabric is cut, a missing repeat or reversed nap may be impossible to repair.
Vertical repeat rounds every drop upward
A patterned fabric’s vertical repeat is the distance along the roll before the motif repeats. For adjacent drops to align, each cut typically begins at a compatible motif position. The raw default length is 84 finished + 8 top + 6 bottom = 98 inches. With an 18-inch repeat, 98 ÷ 18 = 5.444, so each drop rounds to six repeats, or 108 inches.
That adds 10 inches per drop and 30 inches across three drops. The calculation assumes the first usable motif start needs no additional leading waste beyond contingency. Real matching may require an extra repeat at the beginning, especially when centering a dominant motif, correcting a cut edge, or avoiding a flaw.
Horizontal repeat is not calculated. Plaids, stripes, half-drop designs, large medallions, directional scenes, and motifs centered on each panel can require more width or a different seam plan. Obtain the manufacturer’s repeat statement and inspect the physical cloth.
Worked 60-inch curtain pair
The finished treatment covers a 60-inch track and uses two panels at a target 2.0× fullness. Target flat width is 120 inches, or 60 inches per panel. With 54 usable inches across the fabric, three drops are required. For a symmetrical pair, a common conceptual allocation is 1.5 widths per panel, but the workroom must define how the center width is split and where seams fall.
Each panel finishes 84 inches long. Adding an 8-inch top allowance and 6-inch hem gives 98 inches. An 18-inch repeat rounds this to 108 inches. Three drops × 108 inches = 324 inches, and 324 ÷ 36 = 9 yards base.
Ten percent contingency brings the plan to 9.9 yards. If the retailer cuts in one-eighth-yard increments, round 9.9 up to 10.0 yards. The displayed 0.1-yard surplus is only 3.6 linear inches and is not an extra pattern repeat; additional matching or damage risk may justify more.
Header, hem, return, and overlap
The top allowance must reflect the actual construction: rod pocket, casing, grommet, tab, pinch pleat, ripplefold, pencil pleat, cartridge pleat, rings, hooks, tape, buckram, or another system. Hardware spacing and fullness may be prescribed by the heading supplier. Do not use the default eight inches without checking.
The bottom allowance depends on single or double turn, weighted hem, lining, interlining, fabric body, and desired fall. Side hems consume width, not length, and are assumed inside the usable-width decision. Returns wrap toward the wall; overlaps close at the center. Add them to required coverage or allocate them separately before calculating drops.
Floor, sill, apron, radiator, furniture, baseboard, uneven ceiling, and rod level affect finished length. Measure at multiple points after hardware is installed. Decide whether the treatment kisses, breaks, puddles, or clears the floor and document the reference.
Fabric preparation and shrinkage
USU Extension advises washing appropriate fabrics before cutting to address shrinkage and excess dye, then straightening and pressing. Drapery fabrics may instead require professional cleaning, steaming, or no preshrink under manufacturer instructions. Test a sample; do not wash fabric that is not washable.
Contingency can cover some shrinkage uncertainty, but known shrinkage should be calculated explicitly. If a test shows three percent length shrinkage, increase the required pre-treatment cut accordingly before repeat rounding. Lining and face fabric can shrink differently, causing sagging or cupping.
Let fabric relax after unrolling. Verify grain and pattern square. Some printed motifs are not perfectly aligned to the weave; decide which visual reference controls and obtain client/workroom approval.
Workroom verification checklist
Site
Confirm installed hardware, coverage, center, stack-back, returns, overlap, obstacles, floor variation, mounting safety, and operating clearance.
Fabric
Confirm usable width, vertical and horizontal repeats, direction, nap, shrinkage, care, flame or code needs, dye lot, flaws, and stock.
Construction
Confirm panels, seams, side hems, header, bottom hem, lining, interlining, weights, pattern placement, trim, hooks, and labels.
Cut
Draw every drop, reserve match waste, label sequence and orientation, inspect before cutting, and reconcile actual remaining yardage.
When to calculate parts separately
Different-width panels, asymmetrical windows, corner installations, bay windows, doors, tiebacks, valances, cornices, swags, cascades, pelmets, and shaped hems need component takeoffs. Calculate each unique rectangle or pattern-matched drop, then combine before contingency and purchase rounding.
Lining and interlining require their own usable widths, cuts, hems, and shrinkage. Do not assume face-fabric yardage equals lining yardage. Trim is usually calculated from finished edges plus joins and pattern alignment, not from fabric yards.
Curtain fabric FAQs
Why does gross fullness exceed my target?
Fabric is cut in whole usable widths. Rounding 2.222 widths up to three creates excess. The workroom trims, seams, splits, or allocates it according to the design.
What if the fabric has no vertical repeat?
Enter zero. The calculator will use raw cut length, but still allow for straightening, shrinkage, flaws, motif placement, and contingency.
Does the result include lining?
No. Calculate lining and interlining separately with their own widths, cuts, hems, shrinkage, and construction.
Can fabric be railroaded?
Some fabrics can be turned so width runs vertically, but direction, motif, nap, strength, and manufacturer guidance control. This calculator assumes traditional vertical drops.
Is 10 percent contingency always enough?
No. Large repeats, centering, flaws, shrinkage, dye-lot risk, complex seams, or uncertain measurements can require more. Build a physical cutting plan.
Should I round to the retailer’s increment?
Yes, always round upward to an available cut increment. Also check minimum cuts, bolt availability, continuous length, returns, and remnant policies.
Confirm the finished panel width and drop with the curtain size calculator before adding hems, headings, repeats, and pattern-matching allowance.
References
These U.S. sewing education and measurement sources support fabric widths, fullness concepts, preparation, straightening, and yard conversion. Drapery hardware and fabric manufacturer instructions remain project-specific.
- Utah State University Extension — fullness, width, preparation, and yardage planning
- Utah State University Extension — fabric widths, grain, straightening, and preparation
- Utah State University Extension — textile repetition and seam matching
- National Institute of Standards and Technology — length units