Mitered corners fold fabric at a 45-degree angle so the seams meet invisibly inside the corner

A mitered corner is a fold where two seams meet at a 45-degree angle inside the corner, leaving the outside edge flat and seamless. On a napkin, this means the hem turns the corner without a bulky overlap or visible stitching on the front. The technique requires marking a diagonal line, folding twice, and stitching along that line before trimming and turning the corner right-side out.

The process takes practice but becomes faster once you understand the fold. Most napkins use a quarter-inch or half-inch hem, and the mitered corner works the same way regardless of hem width — you just scale the measurements to match.

Key Takeaways

  • Mark a diagonal line from the inside corner at a 45-degree angle, using a ruler and fabric pencil or chalk.
  • Fold the hem allowance down on two adjacent sides, then fold the corner itself along your diagonal line and stitch it closed before trimming.
  • Trim the corner seam to one-eighth inch after stitching, then turn the hem to the back and press flat.
  • The finished corner should show no stitching or seams on the front of the napkin.

Measure and mark the diagonal line at each corner

Start with a napkin cut to finished size plus hem allowance on all sides. If you want a half-inch finished hem, cut the napkin one inch larger than your target size on all edges. At each corner, you need to mark where the two hem lines will meet at a 45-degree angle.

Lay the napkin wrong-side up on a flat surface. Using a ruler and fabric pencil or tailor's chalk, draw a diagonal line from the inside corner (where the two hem allowances meet) outward toward the raw edge. The line should be at exactly 45 degrees — if your hem allowance is half an inch, the diagonal line runs from the corner point outward at 45 degrees. A straightforward way to get the angle right: measure half an inch down from the top edge and half an inch in from the side edge, then draw a line connecting those two points to the corner. That line is your 45-degree angle.

Repeat this marking at all four corners. Use a ruler to keep the lines straight and consistent.

Fold and stitch the corner seam

Fold the hem allowance on one side of the napkin toward the wrong side, pressing it flat with your fingers or iron. Then fold the hem allowance on the adjacent side the same way. The two folded edges will overlap at the corner, forming a triangle of fabric that sticks out beyond where the two hems meet.

Now fold that corner triangle along your marked diagonal line, wrong sides together, so the two raw edges of the corner align. Pin this fold in place. You should now see your diagonal line clearly on the outside of the folded corner.

Stitch along the marked diagonal line using a straight stitch and matching thread. Start at the inside corner point and stitch outward toward the raw edge. Use a short stitch length — around 1.5 to 2 millimeters — to keep the seam strong. Stitch all the way to the edge of the fabric.

Trim the corner and turn the hem right-side out

After stitching, trim the corner seam allowance down to one-eighth inch from the stitching line. This removes bulk so the corner lies flat when you fold the hem to the back. Use sharp scissors or a rotary cutter and ruler to keep the trim straight and even.

Carefully turn the corner right-side out by pulling the hem allowance to the back of the napkin. The corner should fold smoothly without puckering. If it resists, you may have trimmed too little — go back and trim a bit more. Press the corner flat with an iron, making sure the fold sits exactly at the edge of the napkin.

Repeat this process at all four corners before you finish the hem edges.

Fold and stitch the hem edges

Once all four corners are mitered and pressed, fold the hem allowance to the back of the napkin on all four sides. The mitered corners should fold smoothly without bunching. Press the entire hem flat with an iron.

Stitch the hem down using a blind stitch (also called a ladder stitch or slip stitch) if you want the stitching to be invisible from the front. A blind stitch runs inside the fold of the hem, catching only a thread or two of the napkin body with each stitch. Alternatively, use a straight stitch one-eighth inch from the inner fold of the hem for a more visible but faster finish.

Stitch all four sides, including around the mitered corners. At each corner, your stitching will follow the fold you already created, so the corner should stay in place without extra pinning.

Press and check the finished corners

After stitching the hem, press the entire napkin with a hot iron to set the folds and smooth out any wrinkles. The front of the napkin should show no stitching, no seams, and no raw edges at any corner. The back will show the hem stitching and the mitered seams inside the fold.

If you see puckering or the corner does not lie flat, the most common cause is that the diagonal line was not at exactly 45 degrees, or the corner was not trimmed enough. On your next napkin, double-check the angle with a ruler before stitching.

Common mistakes and how to avoid them

The most frequent error is marking the diagonal line at the wrong angle. If the angle is too steep or too shallow, the corner will not fold flat. Use a ruler every time — do not estimate the 45-degree angle by eye. A second common mistake is not trimming the corner seam small enough. Leaving too much bulk in the corner makes it impossible to fold the hem smoothly to the back. Trim to one-eighth inch and you will see the difference.

Another issue is stitching the diagonal line too close to the corner point. If you start your stitch right at the inside corner, the seam can tear when you turn the corner. Start your stitch about one-eighth inch away from the point and stitch outward. This gives the corner enough fabric to hold the seam without stress.

Frequently Asked Questions

What if my diagonal line is not perfectly straight?

A slightly wavy line will still work, but the corner may not fold as smoothly. For your next napkin, use a ruler and mark the line in one continuous motion rather than in sections. If the line is already marked and you are ready to stitch, follow it as closely as you can — the finished corner will still look neat from the front.

Can I use a sewing machine for the blind stitch?

Yes. Most modern machines have a blind stitch setting that mimics a hand-sewn ladder stitch. Use a blind stitch foot (also called a blind hem foot) and match the stitch width and length to your machine's manual. Test the stitch on a scrap of fabric first to make sure the needle catches the hem fold correctly.

How do I know if my hem allowance is the right size?

The hem allowance should be twice the width of your finished hem. If you want a half-inch finished hem, cut the napkin one inch larger than your target size. If you want a quarter-inch hem, add half an inch. This gives you enough fabric to fold twice without running out of material at the corners.

What happens if I stitch the diagonal line in the wrong direction?

The direction does not matter — the seam will be the same either way. What matters is that you stitch along the marked line and trim the excess. Stitch from the inside corner outward, or from the edge inward; the result is identical.

Do I have to use a blind stitch for the hem, or can I use a regular straight stitch?

You can use either. A blind stitch hides the stitching inside the fold, so it is invisible from the front. A straight stitch one-eighth inch from the inner fold is faster and still looks neat, though the stitching line is visible from the back. Choose based on how much time you have and how formal the napkins need to look.