Corner & Miter Calculator

What Are Mitered Corners?

Mitered corners are border corners where two strips meet at a 45° angle, creating a professional frame-like appearance. Unlike butted corners where one border simply overlaps another, mitered corners require precise cutting and sewing but result in a more elegant, polished finish.

Mitered corners are especially important for directional fabrics (like stripes or florals) because they allow the pattern to flow naturally around all four corners of the quilt without disrupting the visual flow.

Why Use Mitered Corners?

Benefits of Mitered Corners

Professional appearance: Creates a picture-frame effect around your quilt
Pattern continuity: Essential for directional prints and stripes
Symmetry: All four corners look identical
No bulk: Even distribution of fabric at corners
Traditional technique: Used in fine quilting and heirloom pieces

When to Use Butted Corners Instead

For beginner quilters still mastering basic techniques
When using non-directional, busy prints where miter seams won't show
For quick utility quilts where speed is more important than finish
When working with very wide borders that make mitering difficult

Understanding Miter Geometry

All mitered corners on square quilts are cut at exactly 45°. This is because the corner of a square is 90°, and the miter line bisects this angle (90° ÷ 2 = 45°). The math is consistent regardless of border width.

Key Measurements

Miter Allowance: Extra fabric needed at each end of a border strip, equal to the border width
Miter Hypotenuse: The length of the 45° cut line, calculated as border width × √2 (approximately 1.414)
Total Strip Length: Quilt edge + (2 × border width) + (2 × miter allowance)

Straight Grain vs. Bias Borders

Straight Grain Borders

Pros: Easier to cut, less fabric needed, more stable, less stretching

Cons: May require piecing for long strips, directional patterns may not align perfectly at miters

Best for: Non-directional prints, beginners, most quilts

Bias Cut Borders

Pros: Better for directional prints, easier to miter stripes, provides "give" for fitting

Cons: Requires significantly more fabric (up to 40% more), edges stretch easily, more difficult to handle

Best for: Striped fabrics, curved quilt edges, showpiece quilts

Common Miter Mistakes

Not stopping stitching at the exact seam allowance

Solution: Measure and mark ¼" from the corner before you start sewing. Some quilters place a pin exactly at this point.

Cutting the 45° angle incorrectly

Solution: Use a ruler with a 45° line, or use the corner of a square ruler. Double-check your angle before cutting.

Stretching borders while sewing or pressing

Solution: Pin carefully, sew with borders on top (against feed dogs), press gently without pulling.

Not matching centers

Solution: Mark the center of each border strip and each quilt edge. Pin centers together first, then ends, then ease in between.

Uneven border widths

Solution: Measure your quilt through the center (not along edges which may have stretched). Cut all four border strips before attaching any.

Working with Directional Prints

Directional fabrics (stripes, florals with a clear up/down direction) require special planning for mitered corners:

Decide on pattern direction: Determine which way the pattern should flow on each side of the quilt (usually same direction on opposite sides)
Add extra fabric: You'll need extra length to match patterns at miter seams, sometimes 6-12" extra per strip
Cut borders carefully: Cut all four borders with the pattern running in your chosen direction
Audition corners: Before sewing, lay out all four strips to see how patterns will meet at corners
Match at miters: When drawing your 45° miter line, adjust so the pattern elements align on both sides of the miter seam

Note: For complex directional prints or stripes, consider using bias-cut borders which make pattern matching at corners much easier, though they require significantly more fabric.

Multiple Mitered Borders

When adding multiple mitered borders (like a narrow inner border and wider outer border), you have two options:

Method 1: Miter Each Border Separately

Add and miter the first border completely, then add and miter the second border.

Pros: Easier for beginners, each border independent
Cons: More seams, more time-consuming

Method 2: Sew Borders Together First

Sew border strips together lengthwise before attaching to quilt, then miter the combined unit.

Pros: Faster, fewer seams, borders perfectly aligned
Cons: Requires more skill, must handle wider strips

Tools for Perfect Miters

Rotary cutter and mat: For accurate cutting of border strips
Long quilting ruler: With 45° angle line marked (essential)
Fine pins: To hold miter seams in place without distortion
Marking pencil or pen: To draw the 45° miter line
Iron and pressing surface: For careful pressing without stretching
Square ruler: To verify corners are square after mitering

Quilt Dimensions (before borders)

Mitered Borders

Fabric Settings

About Mitered Border Corners