Here is a tutorial to make a quilt border with a mitered corner. It looks complicated, but it is really easy.
Width of Border Fabric:
Choose the width of your border. For example, the chevron border above is 6" wide.
The Length of the Border Fabric:
length of the side of the quilt top (green section below)
+ 2 times the width of the border
+ 10 extra inches (for seam allowance, mitering, and extra)
For example, the side of the quilt center above is 55". The length of the chevron fabric cut for the border would be 55 + 6 + 6 + 10 = 77".
1. Center the border with the body of the quilt top.
2. Place them together with the right sides facing each other. Sew the two together with a 1/4 inch seam allowance. The quilt center should be on top and the border on bottom (so you will be looking at the back of your quilt top as you stitch). Make sure you start and stop stitching 1/4 inch from the edge of the main body of your quilt (sew the pink line in the green section above). This is an important part of getting the corner points and seams in the right place.
3. Repeat step 2 for the next side. Be sure and pull the extra from the first border out of the way (the grey section above). Pin it back if it helps. Remember to start and stop 1/4 inch from the edge (where the seam from the other sides ends). Continue repeating these steps until all four sides are completed. The seams will meet up 1/4 inch from each corner, but will not cross over each other.
4. After sewing all four borders on, iron and press the seams open. For the corner seams, fold the top in half to form a triangle. Make sure all the seams and edges match up neatly. Spread the borders out and line them up with right sides facing each other.
(Here is an example)
5. Line up a ruler with the folded edge of the quilt straight out through the borders. Draw a line using a pencil or a quilt marker.
6. This is where you will stitch your seam. Place a couple of pins along the line to hold everything in place. Remember to stop where the previous stitching stopped (Where the arrow on the farthest right is pointing. This will ensure that you end up with a neat pretty corner. Be sure and back stitch here to lock in the stitches.
(close up of where to stop and back stitch)
7. Flatten out the quilt top and make sure everything looks accurate. If you are happy with the results, iron the seams flat and trim the seam allowance to 1/4 inch.
If you have any questions, feel free to message me!