Quilt Mitered Border Calculator: 45 Degree Border Fabric and Yardage

Work out mitered borders before you cut. Enter your quilt top size, border width and fabric width, and see finished size, mitered strip lengths, strips needed and yardage, with the formula in steps.

Calculate your mitered border

Quilt top width in

Quilt top length in

Border width in

Border width is the finished width of one border, on each side of the top.

Fabric width

Seam allowance for joined strips in

Seam allowance is used at each miter end, and when strips are joined end to end. It is the amount lost at each join.

This calculator works out mitered borders only, with 45 degree corners. For square corners, use the Border Calculator.

Your result

Enter your measurements, then calculate.

How the calculator works

Step 1: Finished size

Finished width equals top width plus 2 times border width. Finished length equals top length plus 2 times border width. Border width is added on each side, so it is counted twice.

Step 2: Mitered strip lengths

Each mitered strip is cut longer than the side it borders. The 45 degree corner extends beyond the quilt edge by border width on each end, plus seam allowance at each miter end. Side strip cut length equals top length plus 2 times border width plus 2 times seam allowance. Top and bottom strip cut length equals top width plus 2 times border width plus 2 times seam allowance.

Step 3: Total strip length and strips needed

Total strip length equals 2 times side strip cut length plus 2 times top and bottom strip cut length. If total length fits in one fabric width, you need 1 strip. If not, each extra strip adds fabric width minus seam allowance, because seam allowance is lost at each join. Strips are rounded up.

Step 4: Yardage

Fabric length to buy equals strips times cut width. Cut width equals finished border width plus seam allowance on both sides, because each strip loses one seam allowance where it joins the quilt top and one where it joins the next border or binding. Exact yardage equals fabric length divided by 36 in inch mode. Yardage to buy is exact yardage rounded up to the nearest 1/8 yard. In centimetre mode, metres to buy are rounded up to the nearest 0.1 metre. The unit toggle changes all inputs, outputs and rounding together.

Assumptions, shown next to the result

Fabric width is the nominal width. Seam allowance applies at miter ends and at strip joins. No extra is added for cutting mistakes or shrinkage. This calculator is for one mitered border. For more than one border, calculate the first border, then use its finished size as the top size for the next border.

Straight borders and mitered borders are different

Straight borders meet at square corners. Mitered borders meet at 45 degree corners, and they need extra length for the miter. Do not use straight border lengths for a mitered border, or corners will come up short. This calculator gives mitered lengths only.

Yardage chart by quilt size

This chart uses the same formula as the calculator: 4 inch border width, 44 inch fabric, 0.5 inch seam allowance, yardage rounded up to the nearest 1/8 yard. Yardage matches the straight border chart for these sizes, because strip count is the same. Mitered strip lengths are longer, so for some sizes a mitered border will need an extra strip.

Quilt size	Top size	Finished size	Strips	Yardage to buy
Baby	36 by 48 in	44 by 56 in	5	0.63 yards
Lap	50 by 60 in	58 by 68 in	6	0.75 yards
Twin	68 by 88 in	76 by 96 in	8	1.00 yard
Full	80 by 92 in	88 by 100 in	9	1.00 yard
Queen	90 by 108 in	98 by 116 in	10	1.13 yards
King	108 by 108 in	116 by 116 in	11	1.25 yards

Chart yardage is a guide for the sizes shown. Your exact top size, border width and fabric width may give a different result. Use the calculator above for your own measurements.

Worked example, checked against the calculator

Top size 60 by 72 inches, border width 4 inches, fabric width 44 inches, seam allowance 0.5 inch.

Finished size: width 60 plus 2 times 4 equals 68 inches. Length 72 plus 2 times 4 equals 80 inches.

Side mitered strips: 2 strips, each 72 plus 8 plus 1, which is 81 inches long. Top and bottom mitered strips: 2 strips, each 60 plus 8 plus 1, which is 69 inches long. Total strip length: 2 times 81 plus 2 times 69 equals 300 inches.

Strips needed: 300 inches does not fit in 44 inches. Each extra strip adds 43.5 inches. Strips equal 1 plus the ceiling of (300 minus 44) divided by 43.5, which is 7 strips.

Fabric length to buy: 7 times 5 inches of cut width equals 35 inches. Cut width equals finished border width 4 inches plus seam allowance 0.5 inch on both sides, which is 5 inches. Exact yardage: 35 divided by 36 equals 0.97 yards. Yardage to buy, rounded up to the nearest 1/8 yard, equals 1.00 yard.

Frequently asked questions

How do I calculate a mitered quilt border?

Add border width to both sides of the quilt top to get finished size. Each mitered strip is cut longer than the side it borders, because the 45 degree corner extends beyond the quilt edge by border width on each end, plus seam allowance at each miter end. Add all four strip lengths, work out strips needed from fabric width, and convert strips times cut width to yardage.

How much fabric do I need for a mitered border?

It depends on top size, border width and fabric width. Use the calculator above with your top size, border width and fabric width. The result shows finished size, mitered strip lengths, strips needed and yardage to buy.

What is the difference between mitered and straight borders?

Mitered borders meet at 45 degree corners, like a picture frame. Straight borders meet at square corners. Mitered strips are cut longer than straight strips, because each end must reach past the corner to form the miter.

Do mitered strips need extra length?

Yes. Each mitered strip needs border width extra on each end for the 45 degree corner, plus seam allowance at each miter end. This calculator adds both, and it shows the cut length for each strip in the result.

Can I add more than one mitered border?

Yes. Calculate the first mitered border, then use the finished size from that border as the top size for the next border. Repeat for each border, one at a time.

Why are mitered strips longer than straight strips?

Because a mitered corner is a diagonal join. The strip must reach past the corner of the quilt top, so the diagonal seam can be sewn and trimmed to a clean 45 degree corner. A straight strip stops at the corner, so it is shorter.

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