The basic corner fold: mitering
A mitered corner is the method that keeps a blanket corner flat and square instead of bunched or lumpy. You fold the fabric at a 45-degree angle, then fold it again so the raw edges line up with the blanket edges. When you sew it down, you get a clean diagonal seam inside the corner that lies flat.
The key is that you are not sewing through four layers of fabric at once. Instead, you fold the corner so that only two layers meet the needle at any point. This is why mitered corners work on blankets—they distribute the bulk evenly and don't create a thick knot of thread and fabric where the corner would bend.
Key Takeaways
- A mitered corner requires you to fold the fabric at a 45-degree angle, then fold again so raw edges align with the blanket edges before sewing.
- Mark a line from the corner point to where your seam allowance ends (usually 5/8 inch) to know exactly where to fold.
- Sew from the corner point outward along the fold, then fold the triangle down and sew the remaining edges to complete the corner.
- Press each fold with an iron as you go so the corner stays crisp and the fabric does not shift while you sew.
Marking and folding the first crease
Lay your blanket flat with the corner you are working on facing you. On the wrong side (the side that will be hidden), use a ruler and fabric pencil or chalk to draw a line from the corner point diagonally outward. This line should run at a 45-degree angle and stop where your seam allowance ends—usually 5/8 inch from both edges.
Fold the corner point down so that the two raw edges (the top and side edges of the blanket) line up exactly with each other. The fold you just made should run along the diagonal line you drew. Press this fold with a hot iron so it holds its shape. This first fold is what creates the 45-degree angle that makes the corner lie flat.
Sewing the diagonal seam
With the corner still folded, sew along the diagonal crease you just pressed. Start at the corner point and sew outward toward the edges of the blanket. Use a straight stitch and a standard seam allowance (5/8 inch is typical). Sew until you reach the point where the fold meets the raw edges—you will see where the fabric naturally ends.
Backstitch at the end to lock the thread. Do not sew past the fold line, or you will catch the blanket body in your seam and create puckering. Once you have sewn the diagonal seam, trim the corner triangle close to the stitching—about 1/4 inch away from the seam. This removes the bulk that would otherwise create a lump.
Folding and pressing the corner flat
Open out the corner so the blanket lies flat again. You will see the diagonal seam you just made running across the corner on the wrong side. Now fold the corner point back on itself so the seam runs along the fold. Press this fold hard with your iron so it sets into the fabric.
What you have now is a corner that looks like a triangle on the wrong side, with the seam hidden inside the fold. The raw edges of the blanket are still exposed on two sides of the corner. This is correct—you will bind or fold these edges as part of finishing the blanket edge, and the mitered corner will sit neatly underneath.
Finishing the blanket edges over the corner
Once all four corners are mitered, you will bind or fold the blanket edges. If you are using binding (a strip of fabric sewn around the perimeter), sew it on as you normally would—the binding will cover the raw edges and the mitered corner will sit flat underneath it. If you are folding the edge over (a straightforward fold-and-stitch finish), fold the edge so it wraps around the corner and sew it down. The mitered corner underneath will keep the corner from bunching as you fold.
Press the finished corner with your iron one more time before you consider it done. A well-pressed corner will hold its shape through washing and use.
What to do if your corner puckers or shifts
If the corner does not lie flat after you have sewn it, the most common cause is that you sewed past the fold line and caught the blanket body in your seam. If this happened, you can carefully pick out the stitches in that area and re-sew, staying closer to where the fold naturally ends.
If the corner shifted while you were sewing, it usually means the fold was not pressed firmly enough before you started. Next time, use a hot iron and hold the fold in place for a few seconds so the crease sets. You can also pin the fold in place before sewing if your blanket fabric is slippery.
Frequently Asked Questions
Do I have to miter all four corners?
Yes, if you want the blanket to look finished and lie flat. Mitered corners are the standard method for blankets because they keep the corners from bunching when the blanket is folded or washed. If you skip mitering, you will end up with thick, lumpy corners.
What seam allowance should I use for the diagonal seam?
Use the same seam allowance as the rest of your blanket—usually 5/8 inch. This keeps the corner consistent with the rest of the edge. If your blanket uses a different seam allowance, use that instead.
Can I miter a corner if the blanket is already partially sewn?
Yes, but it is easier to miter before you sew the blanket edges. If you have already sewn one or two edges, you can still miter the remaining corners by following the same steps. Just be careful not to sew through the edges you have already finished.
Should I press the corner before or after I trim the triangle?
Press before you trim. The press sets the fold so it stays in place while you sew. After you trim, you can press again to make sure the corner is still crisp, but the first press is the important one.
What if my fabric is too thick to fold at a 45-degree angle?
Very thick fabrics like fleece or wool can be difficult to miter because the bulk makes the fold hard to manage. You can use a smaller seam allowance (1/2 inch instead of 5/8) to reduce the amount of fabric in the corner, or you can trim the corner triangle more aggressively before folding. Some sewers skip mitering on very thick blankets and use a straightforward overlap corner instead, though this is less neat.