Bias tape is made of cloth cut at a diagonal angle, or on the bias, with edges folded under. Prepackaged, prefolded bias tape is sold in fabric stores, but you'll need to make your own bias tape if you'd like patterned bias tape or tape matched to the exact color of your project. If you're planning your project, you can determine the yardage of fabric needed to make your bias tape before you go to the store so you don't buy more fabric than you really need. If you're planning to make bias tape from fabric you already own, you can determine how much bias tape you can make.
Determine How Much Bias Tape Fabric Will Make

Determine how wide your bias tape strips must be.

Measure the size of your fabric in inches. Write down the length and width of your fabric. If your fabric is not rectangular, you may need to divide it into two imaginary rectangles and measure each separately.

Calculate the area of your fabric by multiplying the length by the width. For example, if your fabric is 24 inches long and 44 inches wide, you would multiply 24 by 44 for a total of 1,056 square inches.

Divide the number of total square inches by the width of the strips you will cut. For example, if you are cutting 2inch strips from 1,056 square inches of fabric, you will cut 528 inches of strips.

Divide the inches of strips to be cut by 36 to determine the yardage of your strips. For example, if you have 528 inches of strips, you will cut 14 2/3 yards of bias strips.
Determine How Much Fabric to Buy for Bias Tape

Determine how wide your bias tape strips must be.

Calculate how many yards of bias tape you will need. For example, a 36inch square baby quilt will need 1 yard of bias tape on each side, plus a little extra for overlap, or perhaps 4 1/2 yards of bias tape total.

Multiply the yardage by 36 to determine how many inches of bias tape strips to cut. For example, if you need 4 1/2 yards of bias tape, multiply 4 1/2 by 36 inches to get 162 inches.

Multiply the total inches of bias strips needed by the width of the strips to determine the total square inches of fabric you will need. If you will be cutting 4inch strips, you would multiply 162 by 4 for a total of 648 square inches.

Find out the width of the fabric you plan to cut into bias tape.

Divide the square inches by the width of your fabric to determine how many inches of fabric you will need cut. Round the resulting number up to the nearest whole inch. If the fabric you will cut into bias tape is 43 inches wide and you need 648 square inches of bias tape, you would divide 648 by 43 for a total of 15.07 inches needed. Round 15.07 up to 16 inches.

Round the inches needed to be cut up to the nearest basic fraction of a yard. Fabric is measured in standard fractions of eighths, quarters, thirds and halves, so 16 inches is 0.44 yards. The next standard cutting width for fabric after 0.44 yards would be 0.5 yards, or 1/2 yard. Purchase at least 1/2 yard of fabric to make your bias tape.
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