About the Quilt Backing Calculator
This quilt backing calculator works out how much fabric you need for the back of a quilt and how to piece it. Enter the finished size of the quilt top, the extra backing you want around each edge for quilting, and the usable width of your fabric. It returns the yardage to buy, the number of panels, the number of seams and the final backing size.
Standard quilting cotton is only about 42" wide once the selvages are trimmed, so most quilts larger than a baby quilt need two or three panels sewn together. The calculator checks both layouts — panels running the length of the quilt (vertical seams) and panels running across it (horizontal seams) — and picks the one that uses less fabric unless you choose a direction yourself.
Long-arm quilters usually ask for 4" to 6" of extra backing on every side; domestic machine quilting often needs only 2" to 4". If you use 108" wide backing fabric, set the usable width to about 106" and you will often need a single panel with no seams at all.
With the default inputs, the backing fabric to buy is 3.875 yd. Change any value above to recalculate instantly.
How to use the quilt backing calculator
- 1Measure the finished quilt top width and length.
- 2Enter the overhang your quilter asks for (often 4" per side).
- 3Enter the usable fabric width — 42" for standard cotton or about 106" for wide backing.
- 4Leave seam direction on “whichever uses less fabric”, or force a direction.
- 5Buy the yardage shown and cut the listed number of panels.
Formula and method
First the backing size is found by adding the overhang to every side of the quilt top. For each layout the calculator finds the fewest fabric panels whose combined width covers the backing, allowing for the fabric lost in each seam (twice the seam allowance, because both panels give up that much). The panel length is the other backing dimension.
Vertical seams mean panels as long as the backing; horizontal seams mean panels as long as the backing is wide. Fabric needed is panels × panel length, converted to yards and rounded up to the nearest ⅛ yard — the smallest cut most shops sell. Pre-washing can shrink cotton by 3–5%, so buy a little extra if you pre-wash.
- W, L
- Quilt top width and length
- o
- Extra backing on each side
- u
- Usable fabric width (selvages removed)
- s
- Seam allowance per side
- p
- Number of panels
Worked examples
60" × 72" throw with 42" fabric
With 4" extra on each side the backing must be 68" × 80". Two 42" panels joined with a 1" seam give 83", enough for either direction. Horizontal seams need two 68" panels (136" = 3.78 yd) versus two 80" panels (160" = 4.44 yd) for vertical seams, so buy 3 7/8 yd.
Queen 90" × 108", long-arm overhang of 5"
The backing must be 100" × 118". Vertical seams need three panels (3 × 42 − 2 = 124" ≥ 100") of 118" each, 354" or 9.83 yd. Horizontal seams also need three panels, but each only 100" long: 300" or 8.33 yd. The calculator picks horizontal seams and rounds up to 8 3/8 yd.
Same queen quilt on 108" wide backing
With 106" of usable width, one piece covers the 100" backing width, so you need a single 118" length: 3.28 yd, rounded up to 3 3/8 yd. Turning it the other way would need two seamed 100" panels (5.56 yd), so the seamless layout wins.
Frequently asked questions
How much bigger should quilt backing be than the top?+
Most long-arm quilters ask for 4" to 6" extra on every side (8–12" total in each direction) so the quilt can be clamped to the frame. For quilting on a home machine 2" to 4" per side is usually enough.
How much backing do I need for a queen quilt?+
A typical 90" × 108" queen quilt with 4–5" overhang needs about 8 1/4 to 8 3/8 yards of 42" cotton pieced with three panels and horizontal seams, or about 3 1/4 to 3 3/8 yards of 108" wide backing with no seams.
Should backing seams run vertically or horizontally?+
Either works structurally. Horizontal seams often use less fabric on wide quilts, while vertical seams are traditional and some long-arm quilters prefer them because they load evenly on the frame. Ask your quilter, or let the calculator choose the cheaper option.
What seam allowance is used for quilt backing?+
A 1/2" seam is common for backing because it is stronger and easy to press open. Always trim the selvages first — they are tightly woven and can pucker after washing.
Is wide backing fabric worth it?+
For quilts wider than about 80", 108" wide backing usually costs less overall and saves sewing seams, although the selection of prints is smaller than standard quilting cotton.