An 18×18 pillow cover uses an 18-inch square front panel and two overlapping back pieces, stitched together with a 1/4-inch seam allowance.
The back overlap is where most first attempts go wrong: cut that opening too narrow and the pillow form works its way out through the gap within a week. Get the back measurements right, though, and an envelope closure skips zippers and buttons entirely. Here is the full cut list, the sewing order, and the small habits that keep corners sharp.
How Much Fabric You Need For An 18×18 Cover
The two-piece back is more common in tutorials and easier to press flat.
- Front: one piece cut 18×18 inches
- Back option A: two pieces cut 18×13 inches each
- Back option B: two pieces cut 18×11 inches each
- Seam allowance: 1/4 inch, used on every stitched edge
- Back hem: a double-fold hem about 1/2 inch wide on the inner edges
Larger back pieces equal more overlap. If your pillow form is plump or overstuffed, go with the 18×13 version; 18×11 leaves a slimmer envelope that can gap open on a thick insert.
The Sewing Steps In Order
The sequence matters more than the speed: hem the back opening edges first, layer the pieces, then sew one continuous loop around all four sides.
- Press a double-fold 1/2-inch hem along one long edge of each back piece, then stitch it down. This raw edge becomes the opening edge and never gets caught in the outer seam.
- Lay the 18×18 front panel right side up on your work surface.
- Place back piece one right side down on top, aligning it with the left raw edges.
- Place back piece two right side down on top, aligning it with the right raw edges. The two hemmed edges overlap in the middle.
- Clip or pin all four sides, keeping the overlap centered.
- Sew around the entire perimeter with a 1/4-inch seam allowance, backstitching at the start and finish.
- Trim the corners diagonally, stopping short of the stitching line by about 1/8 inch.
- Turn the cover right side out, push the corners out with a blunt tool like a chopstick, and press the seams flat.
Once the cover is turned and pressed, the envelope opening sits at the back and the front reads as one clean square. Insert the 18×18 form through the gap and the cover is done.
Mistakes That Ruin The Fit
- Unhemmed back edges. Sewing the cover closed with raw back edges means the fabric frays with every insert and removal. Hem first, always.
- Clipping through the seam. A corner cut that nicks the stitches opens a hole on the very first turn. Leave a small gap between your scissors and the thread line.
- Too little overlap. The Spruce Crafts tutorial on making pillow covers and the Instructables envelope pillow cover walkthrough both use an overlap wide enough to keep the form enclosed.
- Drifting seam allowance. Sewing closer to the raw edge than 1/4 inch shaves the finished cover down, and a snug pillow form then strains every seam.
Sizing works on the same principle: a cover cut larger than the insert looks baggy, while one cut smaller is a fight to close. Measure your pillow form seam to seam, then add your seam allowances to that number. If you would rather skip the sewing machine altogether, a tested roundup of ready-made 18×18 pillow covers covers the store-bought options.
| Construction Choice | What It Changes | Best For |
|---|---|---|
| Two 18×13 back pieces | Roughly 8 inches of total overlap | Thick or overstuffed inserts |
| Two 18×11 back pieces | About 4 inches of overlap | Standard 18×18 forms |
| Single 18.5×42 rectangle | One fold, one seam line to match | Fastest cutting with no pattern |
| 1/4-inch seam allowance | Sets the finished size and corner bulk | Every envelope cover |
| Double-fold 1/2-inch hem | Encloses the back raw edges | The opening side of each back piece |
| Blunt-tool corner turn | Sharp corners without popped stitches | Before pressing the finished cover |
FAQs
Do I need a zipper for this closure style?
No. The overlap in the back holds the insert in place without any hardware, which is why envelope covers are the most common style in written tutorials. If your inset is unusually slick or heavy, add a snap or a short strip of hook-and-loop tape at the opening center to keep the panels from shifting.
What if the cover came out slightly smaller than the insert?
Two fixes work. First, press the cover flat and stretch the seams with steam, which buys back a small amount. A cover that is too snug strains at the corners.
Should I prewash the fabric before cutting?
Yes, if the finished cover will ever be washed. Cotton shrinks noticeably on the first wash, and a cover cut from unwashed fabric can shrink to the point of not fitting its insert. Wash and dry the yardage the same way you plan to launder the finished cover, then press it flat before cutting.
References & Sources
- The Spruce Crafts. “How to Make a Pillow Cover.” Source for the 18×18 front-and-back cutting method and hem allowances.
- Instructables. “How to Sew an Envelope Pillow Cover.” Source for the overlapping back-piece measurements and sewing order.
