Mitre versus Non-Mitre

To determine how much yardage is needed for a border, the border calculator needs to know two things:
  1. Whether the corners of the border are to be mitred, and
  2. Whether the border strips will be pieced using a mitre cut or a non-mitre cut.
In both cases, a mitre cut is cut at a 45 degree angle whereas a non-mitre cut is made perpendicular to the lengthwise direction of the border strip.

A non-mitred corner is shown below on the left and a mitred corner is shown below on the right. (The lines in the pictures of the borders show where the seams are.) Slightly longer border strips must be cut for mitred corners than for non-mitred corners.
Non-Mitred Border Picture   Mitred Border Picture
Non-Mitred Corner   Mitred Corner

The border strips that you cut need to be pieced together. This can be done in an "end-to-end" or "on the diagonal" fashion as shown below. (The lines in the pictures depict seams for the pieced border strips.) Piecing "on the diagonal" will require more yardage, particularly for wide borders.
Straight Border Picture             On the Diagonal Border Picture
End-to-End Piecing   On the Diagonal Piecing