How much fabric do I need for quilt backing?

Quilt backing yardage chart (yards)

Sizes are the commonly printed US pattern sizes. Backing is the top plus 4 in on every side (longarm ready). Pieced backings use 42 to 44 in quilting cotton with 40 in usable after the selvages are removed and 1/4 in seams. Wide back is 108 in fabric with 104 in usable. Every amount is rounded up to the next 1/8 yd, the cut most North American shops sell.

Bold is the cheaper pieced layout. "Turned" means the wide back runs sideways, so its print runs across the quilt; that saves fabric whenever the print has no up and down. The king only fits one wide back length turned, and the cal king backing (112 x 108 in) is wider than 104 in both ways, so it takes two lengths seamed, or one length of 118 in (3 m) wide backing if your shop stocks it (check the usable width on the bolt).

Metric backing chart (metres)

Same quilts in centimetres, backing 10 cm larger on every side, 102 cm usable width, 0.75 cm seams, wide back 274 cm with 264 cm usable, rounded up to 10 cm.

How much bigger than the quilt top should the backing be?

Longarm: 4 in (10 cm) on every side, which is 8 in (20 cm) added to both the width and the length. The longarm frame clamps the backing to rollers at top and bottom and holds the sides with clamps. The extra fabric is what those grip, and it gives the quilter room to stitch right to the edge of your top. Many longarm services ask for 4 in or more and a squared backing, so read your quilter's checklist before you cut.

Domestic machine or hand quilting: 2 to 3 in (5 to 8 cm) on every side. Layers shift a little while you baste and quilt, and quilting draws the top in. That margin keeps the backing from ending up short at a corner. If this is your first quilt, take the full 3 in.

Batting is cut to the same size as the backing, so the same margin applies to both.

The backing panel formula

Here is the formula our calculators use (backing_yardage). It works for any quilt and any fabric width.

1. Backing size = top width + 2 x margin, by top length + 2 x margin.
2. Panels for vertical seams = ceil((backing width minus 1/2 in) / (usable width minus 1/2 in)). Each panel is as long as the backing length.
3. Panels for horizontal seams = ceil((backing length minus 1/2 in) / (usable width minus 1/2 in)). Each panel is as long as the backing width.
4. Fabric = panels x panel length for each layout. Buy the smaller one, rounded up to 1/8 yd (4 1/2 in) or 10 cm.

The 1/2 in is the two 1/4 in seam allowances each joined panel loses (in metric, use 1.5 cm for two 0.75 cm seams). "Ceil" means round up to a whole panel: you cannot buy 1.7 panels.

Why compare both ways? The panel count is often the same, but the panel length is not. A throw backing of 68 x 78 in needs two panels either way. Vertical panels are 78 in long; horizontal panels are 68 in long. Same seams, 20 in less fabric.

Worked example: throw, in inches

Top 60 x 70 in, quilted on a longarm.

1. Backing = 68 x 78 in.
2. Vertical: ceil((68 minus 1/2) / (40 minus 1/2)) = ceil(1.71) = 2 panels x 78 in = 156 in (4 1/3 yd). Buy 4 3/8 yd.
3. Horizontal: ceil((78 minus 1/2) / 39 1/2) = ceil(1.96) = 2 panels x 68 in = 136 in (3 7/9 yd). Buy 3 7/8 yd.
4. Choose horizontal and save 1/2 yd.

Quilting it yourself on a domestic machine with a 3 in margin? The backing becomes 66 x 76 in, and horizontal seams take 2 x 66 = 132 in: buy 3 3/4 yd.

Worked example: queen, in inches

Top 90 x 95 in, longarm.

1. Backing = 98 x 103 in.
2. Vertical: ceil(97 1/2 / 39 1/2) = 3 panels x 103 in = 309 in. Buy 8 5/8 yd.
3. Horizontal: ceil(102 1/2 / 39 1/2) = 3 panels x 98 in = 294 in. Buy 8 1/4 yd.
4. Wide back (104 in usable): one length. Keep the print upright and you need 103 in, so buy 2 7/8 yd. If the print can run sideways, 98 in is enough: 2 3/4 yd.

That is 8 1/4 yd of quilting cotton against 2 7/8 yd of wide back, and only one length to square up instead of three panels to join. For queen and king quilts, wide backing is almost always the better buy.

Worked example: metric throw, in centimetres

Top 150 x 200 cm, longarm, quilting cotton with 102 cm usable.

1. Backing = 170 x 220 cm.
2. Vertical: ceil((170 minus 1.5) / (102 minus 1.5)) = ceil(1.68) = 2 panels x 220 cm = 440 cm.
3. Horizontal: ceil((220 minus 1.5) / 100.5) = ceil(2.17) = 3 panels x 170 cm = 510 cm.
4. Choose vertical and buy 4.4 m.

Notice this one flips: the metric throw is long and narrow, so two vertical panels cover the 170 cm width, while the 220 cm length would need three. That is exactly why you calculate both ways every time.

Vertical vs horizontal vs wide back: which should I choose?

Vertical seams run the length of the quilt. The fabric's lengthwise grain runs top to bottom, so a directional print stays upright. They win on twin, king and cal king sized backings.

Horizontal seams run across the quilt. They win on crib, throw, full and queen backings in our chart. The print turns sideways, which only matters for directional prints such as trees, text or animals walking one way.

Wide back (108 in, 274 cm). One length covers any backing up to 104 in (264 cm) in one direction. From a full size up, it is less than half the yardage of a pieced back and has no seams at all. Wide backs also come in 90 in goods (86 in, 218 cm usable), handy for twins.

Our take: for throws and anything smaller, piece the back from quilting cotton; it is a good home for an orphan block or a fat quarter strip down the middle. For full, queen and king, buy wide backing. It is less fabric, less cutting and a flatter back.

Do longarm quilters prefer horizontal seams?

Many do. With horizontal seams the seam runs parallel to the rollers, so the backing winds evenly and tension stays the same across the frame. Vertical seams roll up on themselves and build a slightly thicker band. Preferences vary from quilter to quilter, and plenty load vertical seams happily, so ask yours before you sew.

How to piece a quilt back, step by step

1. Cut the panels to length. Square one end of the fabric first, then cut each panel to the panel length from your calculation.
2. Remove the selvages. Trim about 1/2 to 1 in (1.3 to 2.5 cm) off both edges. Selvages are woven tighter than the rest of the fabric and shrink differently in the wash, which puckers a seam that includes them. Your usable width is what remains, usually 40 to 42 in (102 to 107 cm).
3. Match any print. For a large print, line up the motifs before you pin. It can cost one pattern repeat in length, so buy that extra.
4. Sew the panels together. Right sides together. A 1/4 in (0.75 cm) seam is fine; many longarm services ask for 1/2 in (1.5 cm) on backing seams for strength. In the inch chart above, a 1/2 in seam leaves every panel count unchanged.
5. Press the seams open. Open seams lie flat, spread the bulk and roll evenly on a longarm frame.
6. Square the backing. Fold it in half, then check the corners and edges are at right angles. Trim if needed, keeping the full margin on every side. Longarm quilters especially need straight top and bottom edges to load on the rollers.
7. Mark the top edge with a safety pin if the print has a direction, so your quilter loads it the right way up.

Cut the batting to the backing size

Batting is cut to the same size as the backing: 68 x 78 in for the longarm throw above. Unfold it a day ahead or relax it as the package says. If one piece is too narrow, butt two straight cut edges together and join them with a wide zigzag or batting tape. Never overlap batting; the ridge shows through the quilt.

Mistakes and fixes

Using the full 44 in width in the maths. Bolts say 42 to 44 in, but after selvages and a straightening cut you have about 40 in. Fix: calculate with 40 in (102 cm) usable and you will never be short by a sliver.

Adding 4 in in total instead of on every side. A 60 x 70 in top with a 64 x 74 in backing leaves the longarm nothing to clamp. Fix: add the margin twice to each measurement, 8 in (20 cm) in total.

Leaving the selvages on. They pucker the seam after washing. Fix: trim them off before you sew.

Turning a directional print sideways. Horizontal seams and turned wide backs run the print across the quilt. Fix: for a one way print, use vertical seams or buy the wide back to the full backing length.

Forgetting shrinkage. Prewashed cotton can lose a few percent, and mills differ. Fix: if you prewash backing fabric, buy an extra 1/8 to 1/4 yd (10 to 20 cm) on a pieced back.

Buying exactly to the inch. A shop's cut can be a little crooked. Fix: rounding up to the next 1/8 yd or 10 cm, as in our tables, covers a straightening cut.