Mitred Border Corner Calculator
A mitred corner is where two borders meet at 45° like a picture frame. To make that diagonal the strip has to run past the quilt edge by the border width at each end, plus 5 cm for safety. On a 150 cm side with a 15 cm border, cut 150 + 2 × 20 = 190 cm, mark 20 cm in from each end and stitch only between the marks. The diagonal to cut measures 15 × √2 = 21.2 cm.
Your numbers
Strip for top and bottom
190cm
Strip for the sides
240cm
Mark from each end
20cm
Diagonal cut length
21.2cm
Formula
Strip for top and bottom = Quilt width + 2 × Border width + 10, Strip for the sides = Quilt length + 2 × Border width + 10
Stitching right to the ends of the strip makes the corner impossible to fold. Sew between the two marks only and backstitch at both. The diagonal is on the bias and stretches under the iron, so join the two strips at 45° first and trim the excess afterwards — trimming first cannot be undone.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Quilt width (cm)The finished quilt across, once bound. | 150 | 1 and up |
| Quilt length (cm)The finished quilt along, once bound. | 200 | 1 and up |
| Border width (cm)The border's finished width; it lands on both edges, so the quilt grows by twice this. | 15 | 1 and up |
Step by step
Quick reference table
Results when only Quilt width (cm) changes and everything else stays put.
| Quilt width (cm) | Strip for top and bottom (cm) | Strip for the sides (cm) | Mark from each end (cm) |
|---|---|---|---|
| 75 | 115 | 240 | 20 |
| 113 | 153 | 240 | 20 |
| 150 | 190 | 240 | 20 |
| 225 | 265 | 240 | 20 |
| 300 | 340 | 240 | 20 |
What each result means
| Result | At default values |
|---|---|
| Strip for top and bottom (cm)Cut length for the top and bottom strips, with the mitre waste on both ends. | 190 |
| Strip for the sides (cm)Cut length for the side strips, longer by the quilt's length. | 240 |
| Mark from each end (cm)How far in from each strip end to mark; stitch only between the two marks. | 20 |
| Diagonal cut length (cm)Length of the 45° line at the corner — the border width times √2. | 21.2 |
Common mistakes
Stitching right to the ends of the strip makes the corner impossible to fold. Sew between the two marks only and backstitch at both. The diagonal is on the bias and stretches under the iron, so join the two strips at 45° first and trim the excess afterwards — trimming first cannot be undone.
Glossary
- Quilt width
- The finished quilt across, once bound.
- Quilt length
- The finished quilt along, once bound.
- Border width
- The border's finished width; it lands on both edges, so the quilt grows by twice this.
- Strip for top and bottom
- Cut length for the top and bottom strips, with the mitre waste on both ends.
- Strip for the sides
- Cut length for the side strips, longer by the quilt's length.
- Mark from each end
- How far in from each strip end to mark; stitch only between the two marks.
- Diagonal cut length
- Length of the 45° line at the corner — the border width times √2.
Frequently asked questions
Q. How is Mitred Border Corner Calculator calculated?
Strip for top and bottom = Quilt width + 2 × Border width + 10, Strip for the sides = Quilt length + 2 × Border width + 10 — A mitred corner is where two borders meet at 45° like a picture frame. To make that diagonal the strip has to run past the quilt edge by the border width at each end, plus 5 cm for safety. On a 150 cm side with a 15 cm border, cut 150 + 2 × 20 = 190 cm, mark 20 cm in from each end and stitch only between the marks. The diagonal to cut measures 15 × √2 = 21.2 cm.
Q. Can you walk through an example?
With Quilt width 150cm, Quilt length 200cm, Border width 15cm, the answer is Strip for top and bottom 190cm.
Q. What do I need to enter?
Enter Quilt width, Quilt length, Border width. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Quilt width (cm) moves the answer to Quilt width (cm) 75 → Strip for top and bottom (cm) 115 and Quilt width (cm) 300 → Strip for top and bottom (cm) 340. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Stitching right to the ends of the strip makes the corner impossible to fold. Sew between the two marks only and backstitch at both. The diagonal is on the bias and stretches under the iron, so join the two strips at 45° first and trim the excess afterwards — trimming first cannot be undone.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.