A mitered corner is two fabric edges sewn together at a 45-degree angle so the seams meet invisibly inside the fold

A mitered corner is the technique that lets you fold fabric at a corner without a bulky seam showing on the outside. Instead of sewing two layers straight across the corner (which creates a thick lump), you fold the fabric diagonally so the two seam lines meet at a 45-degree angle inside the fold. The result is a corner that looks crisp and professional—you see it most often on napkins, pillowcases, and the edges of quilts.

The basic idea is straightforward: you mark a diagonal line from the outside corner to the inside corner, sew along that line, trim the excess, and fold the corner closed. The seams end up hidden inside the fold, and the corner lies flat instead of puckering or bunching.

Key Takeaways

  • Mark a diagonal line from the outside corner to the inside corner using a ruler and fabric pencil, then sew along that line before you fold the fabric.
  • Trim the excess fabric close to the seam line, leaving about a quarter-inch, then turn the corner right-side out and press it flat.
  • The two seam lines meet at a 45-degree angle inside the fold, which is what makes the corner lie flat without bulk.
  • Practice on scrap fabric first—getting the angle right takes one or two tries, and mistakes are easier to see on a test piece.

Mark the diagonal line before you sew

Lay your two fabric pieces right sides together, with the corner you want to miter lined up exactly. Use a ruler and a fabric pencil or chalk to draw a diagonal line from the outside corner (where the two edges meet) to the inside corner (where the fold will be). The line should run at 45 degrees—if you are mitering a square corner, the line will go from one corner of your seam allowance to the opposite corner.

For a standard quarter-inch seam allowance, your diagonal line will start at the outside corner and end a quarter-inch away from the inside corner. If you are unsure about the angle, fold the corner in half diagonally and crease it lightly—the crease shows you exactly where the 45-degree line should go. Mark the line clearly so you can see it while you sew.

Sew along the diagonal line with a straight stitch

Set your machine to a straight stitch with a normal stitch length (around 2.5 millimeters). Sew directly along the diagonal line you marked, starting at the outside corner and ending at the inside corner. Backstitch at both ends to lock the seam. Sew slowly and carefully—the accuracy of this seam determines how flat your corner will lie.

If you are mitering multiple corners (like on a napkin or pillowcase), sew all the diagonal seams before you trim anything. That way you can check that all the corners look even before you move forward.

Trim the excess fabric and turn the corner right-side out

Once the diagonal seam is sewn, trim the excess fabric close to the seam line. Leave about a quarter-inch of fabric beyond the stitches—this prevents the seam from unraveling when you turn the corner. Trim both layers of fabric at the same time so they are even. If you are working with a thick fabric, you can trim one layer slightly shorter than the other to reduce bulk in the fold.

Now turn the corner right-side out by pulling the fabric through the opening. Use a point turner or the blunt end of a chopstick to gently push the corner out from the inside. The diagonal seam should now be hidden inside the fold, and the corner should form a sharp point.

Press the corner flat to set the seams

Place the corner on your ironing board and press it with a hot iron (the heat setting depends on your fabric—use the hottest setting safe for your material). Press from the outside, working the corner into a sharp point. The heat and pressure set the seams and help the corner lie flat.

If the corner still looks puffy after pressing, you may have left too much fabric in the seam allowance. For future corners, trim a bit closer to the stitches. If the corner looks sharp but the seams are visible from the outside, you may have sewn too far from the edge—next time, move your diagonal line closer to the outside corner.

Finish the edges if your project requires it

If you are making a napkin or a pillowcase, you will need to close the opening after you turn the corner right-side out. Fold the raw edges of the opening inward by a quarter-inch and press them. Then topstitch (sew a visible line of stitches) around the entire edge, about an eighth-inch from the fold. This seals the opening and holds the mitered corners in place.

If you are mitering the corners of a quilt binding or a facing, you may not have an opening to close—the binding or facing is already attached to the main fabric. In that case, press the corner and move on to your next step.

Common mistakes and how to avoid them

The most common error is sewing the diagonal line at the wrong angle. If your angle is too steep or too shallow, the seams will not meet inside the fold, and the corner will either bunch up or leave a gap. The fix is to mark your line carefully using a ruler, and to test your angle on a scrap piece of fabric before you sew your actual project.

Another frequent mistake is leaving too much fabric in the seam allowance after you trim. This creates a bulge inside the corner that shows from the outside. Trim close to the stitches—a quarter-inch is the maximum you should leave. If you are working with a slippery fabric like silk or satin, use pinking shears to trim the edges so they do not fray as much.

Finally, some people forget to press the corner after turning it right-side out. The iron is what makes the corner look crisp and professional. Without pressing, the corner will look soft and rounded even if the seams are correct.

Frequently Asked Questions

Do I have to use a quarter-inch seam allowance for a mitered corner?

No. The seam allowance can be any width you choose, but a quarter-inch is standard in most sewing projects. Whatever width you use, make sure your diagonal line ends a quarter-inch (or your chosen width) away from the inside corner, not at the corner itself.

Can I miter a corner on fabric that is already sewn to something else?

Yes, but it is more difficult. You will need to unpick the seam at the corner, miter it, and then re-sew the seam. It is much easier to miter before you attach the fabric to anything else. If you are working with a binding or facing, miter it before you attach it to the main piece.

What if my corner does not come to a sharp point after I turn it right-side out?

Use a point turner or chopstick to push the corner out from the inside. If it still will not sharpen up, you may have sewn too far from the outside edge. Next time, move your diagonal line closer to the corner. Press the corner with a hot iron to help it set into shape.

How do I miter a corner on a curved edge?

Curved edges are much harder to miter because the angle changes as you move along the curve. For most projects, you will only miter corners on straight edges. If you need to finish a curved edge, consider binding it instead, which is simpler and looks professional.