Prepping the Backing So It Doesn't Come Up Short
Okay. Your top is done, your batting's picked out. Now we deal with the backing, and this is the lesson where I see people cut corners they shouldn't.
Here's the problem in one sentence: your backing has to be bigger than your top, on all four sides, and "close enough" isn't close enough.
Why this matters more than it seems like it should
When you pin baste, the layers shift. A little bit here, a little bit there, and by the time you're quilting the last quarter of the top you can run out of backing on one edge before you've finished. I've seen it happen at the kitchen table of someone I was teaching. There's no fixing it mid-quilt. You either stop with an unquilted strip along the edge or you piece in an emergency scrap of backing fabric that never quite matches, and you know it's there every time you look at that quilt.
So we build in a margin. For lap-sized work, I want at least 4 inches of extra backing on every side. Some people say 3. I'd rather have too much than stand at my machine doing math with a ruler in one hand.
Measuring your top
Lay your finished top flat. Measure the length and the width at the actual finished edges, not across a wonky spot where a seam pulled things out of square. If your top measures 50 by 60, your backing needs to be at least 58 by 68. That's 4 inches added to each side, 8 inches total added to each dimension.
Write the number down. Don't trust yourself to remember it across a Costco run for fabric. I've done that. I stood in the aisle positive I remembered and I did not.
Piecing the backing
Almost nobody has fabric wide enough for a lap quilt backing off a single width, so you're piecing it. Two options, and I'll tell you which one I use.
You can seam two panels down the middle, one long seam straight through. That works fine and it's the fastest. Or you can do what I usually do, which is put the seam off-center, so it's not running right down the middle of the quilt where it's most likely to show through if your batting's thin or your fabric's light. Doesn't matter much either way functionally. That one's just a preference of mine.
Press that seam open, not to the side, so it lies as flat as possible under the quilting. A bulky seam in the backing behaves the same way a bulky seam in the top does when the needle hits it. It fights you.
The fabric choice itself
This is where anecdote nine comes in, sort of sideways. My daughter picked the fabric for one of my quilts once. Loud, clashing, absolutely nothing I'd have chosen for myself. I let her pick the backing on that one too, actually, and it was this busy floral print that had no business going with the front. It's my favorite quilt I own. It lives on the back of our couch and gets used more than anything else I've made.
I bring that up here because people get precious about backing fabric like it needs to coordinate perfectly with the top, and honestly, it doesn't have to. Nobody sees the two sides at the same time. Pick something you like, pick something on sale, let a kid pick it if you've got one handy. The backing doing its job matters more than the backing being perfectly matched.
One real caution here: avoid anything with a heavy metallic thread or a stiff finish for your backing if this is a quilt you'll actually use and wash. Metallics can be scratchy against skin and some finishes don't soften up in the wash the way you'd hope. Plain cotton, good hand feel, that's what I reach for.
Pressing before you baste
Press the whole backing flat once it's pieced, seam included. Iron out any fold lines from how it came off the bolty or out of the package, because those creases will telegraph through as little ridges once it's pinned and quilted. At our elevation the dry air actually works in your favor here. Fabric presses crisp and stays that way instead of going limp on you, so take advantage of it.
Lay it out somewhere flat before you baste. Floor, big table, whatever you've got. Smooth it out from the center, not just tugged at the corners. If there's a wrinkle trapped in the middle when you pin over it, it's staying trapped.
Before next time
Measure your finished top and figure your backing dimensions with the 4-inch margin on all sides. Get that fabric pieced and pressed before we meet again, because next lesson we're pin basting the whole sandwich and I don't want anyone starting from scratch at the table.