Pattern piece B
Bias tape calculator
How wide to cut the strips for the tape you want, how big a square makes enough continuous bias, and how many strips to cut across the fabric instead.
- Cut strips
- 2 in5.1 cm wide, on the bias
- Square needed
- 16 in40.6 cm each side
- Or cut strips
- 2 strips59 3/8 in each, 1 join
- Fabric to buy
- 1/2 yd0.5 m · cheaper method
Double-fold bias tape, 1/2 in finished: cut bias strips 2 in wide. You need 108 in of tape.
Continuous bias from a square
A 16 in square marks 5 strips about 21 7/8 in long, about 109 5/8 in (278.4 cm) of continuous tape after the two 1/4 in seams. The quick rule, side × side ÷ strip width, says 128 in, which leaves nothing for the seams or the trimmed ends. Fabric used: 16 in.
Strips cut across the fabric
Cut 2 strips at 45° from selvage to selvage, each about 59 3/8 in long, and join them on the straight grain (1 join, each using about 11/16 in): 118 1/8 in (299.9 cm) in all. The first 45° cut takes one fabric width of length, so this uses 47 5/8 in of fabric; buy 1 3/8 yd (1.3 m). The two corner triangles left over are big enough for short pieces or another square.
How the strip width and yardage are worked out
Single-fold tape has both long edges pressed to the middle, so the strip is twice the finished width; that is the rule Clover gives for its bias tape makers. Double-fold tape is single-fold pressed in half again, so the strip is four times the finished width. French binding is a strip folded in half, sewn on with an allowance as wide as the finished binding and wrapped to the back: about six times the finished width. For quilts and thick fabric add a little for the turn of the cloth; C&T Publishing's ¼ in quilt binding is cut 1⅝ in, ⅛ in more than six times.
Continuous bias: cut a square on the diagonal, sew the two straight-grain edges together into a parallelogram, mark strips parallel to the bias edges, sew the other two edges into a tube one strip out of step, and cut round in a spiral. The calculator counts the whole strips that fit after both ¼ in seams. That is why its answer is below the quick rule of side × side ÷ strip width.
Worked example: 108 in of ½ in double-fold tape needs 2 in strips. A 16 in square gives 5 strips about 22 in long, 109½ in in all; a 15 in square falls short at about 102½ in. Cut across 42 in fabric instead, each 45° strip is about 59 in long, so 2 strips and one join cover it, using about 47⅝ in of fabric because the first diagonal cut takes a full width.
Cut strips wins for long lengths of narrow tape on wide fabric; a square wins for short runs or a fat quarter.
Sources
- Clover, Bias Tape Makers: cut fabric on the bias twice the finished width; makers in 6, 12, 18, 25 and 50 mm.
- Sew4Home, How to make continuous bias binding: the square, parallelogram and tube method with ¼ in seams.
- McCall's Quilting via Quilting Daily, How to make continuous bias: square sizes for 110–480 in of 1½–3 in strips, and quilt binding length = 2 × (width + length) + 10 in.
- C&T Publishing, Calculating yardage for bias binding: perimeter + 10 in; 1⅝ in strips for ¼ in double-fold and 1⅛ in for single-fold quilt binding.
Questions
Why does my square make less tape than the formula says?
Side × side ÷ strip width spreads the whole square into tape. In practice two seams take a little from every strip, and the part strip left at the edge is trimmed away. Counting whole strips, as this calculator does, matches what you actually cut.
Do I need bias strips, or will straight-grain strips do?
Bias strips stretch and bend smoothly, so they are needed for curves such as necklines, armholes and round hems. Straight edges, like most quilts, can be bound with strips cut on the straight grain, which use less fabric.
What width should I cut for a bias tape maker?
The size printed on the maker is the finished single-fold width, and Clover's instructions say to cut strips twice that: 24 mm (1 in) strips for the 12 mm maker. Press the result in half again for double-fold tape.
How do I join bias strips?
Cut the strip ends along the straight grain, lay two ends right sides together at right angles, stitch along the grain and press the seam open. The calculator allows for the length each join uses.