MathBench

Quilt Calculator

Enter your quilt top's size — or pick a standard — and get the backing yardage (seamed the thrifty direction), the batting to buy, and the binding strips to cut.

Shopping list

—backing fabric
—batting (precut)
—binding strips
—binding fabric

How this calculator works

Give the calculator your finished quilt-top size — the presets cover the standard bed sizes — and it works out the three finishing purchases. Backing: the quilt plus overhang on every side, pieced from your fabric's usable width, with the seam direction chosen by comparing both layouts and taking the cheaper (the note shows what the other direction would have cost). Batting: the smallest standard precut that covers, in either orientation. Binding: how many strips of your chosen width to cut across the fabric, and the yardage they consume.

The defaults reflect how quilts actually get finished: 4″ overhang because that's what longarm quilters require, 42″ usable width because that's what "44/45″" quilting cotton really delivers, and 2½″ strips because that's the modern double-fold binding standard. Every default is editable when your project differs.

The formula

backing size = (width + 2·overhang) × (length + 2·overhang)
panels       = ⌈backing width ÷ usable fabric width⌉   (both seam
               directions compared; cheaper one reported)
backing yardage = panels × backing length

binding strips  = ⌈(2·(W + L) + 10″) ÷ 40″⌉
binding yardage = strips × strip width

Plain geometry plus quilting-industry conventions: 40″ of usable strip length per width-of-fabric cut, 10″ of extra binding for mitred corners and the final join, and the packaged batting sizes (crib 45×60 through king 120×120) as sold industry-wide and listed in standard quilting references such as the All-in-One Quilter's Reference Guide.

Worked example

Finish a twin quilt, 70″ × 90″ (the default), 4″ overhang, 42″ fabric, 2½″ binding:

  1. Backing size: 78″ × 98″
  2. Seams lengthwise: ⌈78 ÷ 42⌉ = 2 panels × 98″ = 196″ = 5½ yards
  3. Seams crosswise: ⌈98 ÷ 42⌉ = 3 panels × 78″ = 234″ = 6½ yards — lengthwise wins by a yard
  4. Batting: 78 × 98 doesn't fit twin 72×90 — smallest cover is queen 90×108
  5. Binding: perimeter 320″ + 10″ = 330″; ⌈330 ÷ 40⌉ = 9 strips at 2½″ = 22.5″ = ⅝ yard

That batting result surprises people — the overhang pushes a twin quilt past twin batting. It's exactly the kind of arithmetic worth doing before the store trip rather than after.

Assumptions & tips

  • Ask your longarmer before buying backing. Four inches per side is the common requirement, but some machines want more. One text message beats re-piecing a backing.
  • Press backing seams open. A seam pressed to one side makes a ridge the quilting machine feels forever. Open and flat is the workroom standard.
  • Wide backing exists. 108″ quilt-backing fabric eliminates seams entirely — for the twin example, 2¼ yards of wideback replaces 5½ yards of piecing. Price both before cutting.
  • Cut binding on the crossgrain, not the bias — unless your quilt has curved edges. Straight-grain binding is stable and thrifty; save bias binding for scallops.
  • Buy the batting after the top is done. Tops have a way of growing a border in the design process; batting bought early to the planned size becomes batting that almost fits.

Frequently asked questions

Why does the backing need to be bigger than the quilt top?

Because quilting shifts the layers. Basting and quilting draw the top up slightly, and if you send the quilt to a longarm quilter, the machine's frame physically clamps the backing edges — most longarmers require 4 inches of extra backing on every side and will send a too-small backing home. Hand and domestic-machine quilters can get by with 2 to 3 inches per side; the calculator's overhang field covers both.

Which way should the backing seam run?

Whichever direction wastes less fabric — and the calculator compares both. A seam running crosswise often saves a half yard or more on wide quilts. The one rule: press the seam open (not to the side) so it lies flat under dense quilting, and never put a seam exactly down the center fold line where a bed quilt creases most.

How wide should binding strips be?

Two and a half inches is the modern standard for double-fold (French) binding on a quilt with regular batting — it finishes at about ⅜ inch. Sewists who like a skinnier binding cut 2¼; thick battings sometimes want 2¾. The calculator's strip width field feeds straight into the yardage math, so cut whatever your style demands.

What are the standard precut batting sizes?

The industry sells packaged batting as: crib 45×60, twin 72×90, full 81×96, queen 90×108, and king 120×120 inches. The calculator tells you the smallest precut that covers your quilt with overhang — but batting is also sold by the yard off wide rolls, which can waste less on odd sizes. Piecing batting scraps with a wide zigzag is legitimate thrift, not a shortcut.

Does quilting cotton really give 42 usable inches?

Quilting cotton is nominally 44/45 inches wide, but selvages plus shrinkage leave about 40 to 42 usable — which is why this calculator defaults to 42 and why binding strips are figured at 40 inches of usable length each. If you pre-wash, measure your actual width after washing; a border strip planned at 42 that washed down to 41 is a sad discovery mid-project.

Sources

  1. Quilt Size Chart — APQS (American Professional Quilting Systems). apqs.comThe longarm maker's own rule behind the overhang default — on a longarm the backing is typically 6 to 8 inches wider than the quilt top so the machine can stitch off the edges and the side clamps have something to grip — plus the commercially pre-packaged batting sizes this calculator searches.
  2. Hobbs Heirloom Premium 80/20 Cotton/Poly Blend Batting — Hobbs Bonded Fibers. hobbsbatting.comManufacturer's packaged sizes — crib 45×60, twin 72×90, full 81×96, queen 90×108, king 120×120 — the exact list the calculator scans for the smallest precut that covers your quilt plus overhang. The same page lists the 96″ and 120″ rolls behind the "buy roll batting by the yard" fallback when no precut is large enough.
  3. All-in-One Quilter's Reference Tool, Updated Second Edition — Harriet Hargrave, Sharyn Craig, Alex Anderson and Liz Aneloski, C&T Publishing, 2014 (ISBN 978-1-60705-852-6). ctpub.comThe quilting reference this page names for its shared workroom arithmetic: yardage requirements, cutting charts, standard quilt dimensions, and straight-grain versus bias binding methods. Listed under its exact published title, which differs slightly from the name used in the text above.