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Part 5: Understanding seam allowance


What is a seam allowance?

A seam allowance is the distance between the seam line (where you stitch to join two or more pieces of fabric) and the cut edge of the fabric.

How much seam allowance is there in a garment?

Simplicity’s standard seam allowance is 5/8″ (1.5cm). When the seam allowance is more or less than 5/8″ (1.5cm), the amount is specified both on the pattern piece and in the sewing instructions.

Why is 5/8″ (1.5cm) the standard seam allowance?

A 5/8″(1.5cm) seam allowance provides enough “extra” between the seam line and the cut edge of the fabric to make sure that you will safely “catch” the pieces that you are joining together. This is particularly important when working with fabrics that ravel easily. A 5/8″ (1.5cm) seam allowance is also easier to work with when pressing a seam open or topstitching it for a finishing touch. Finally, it also provides you with a small amount of “letting out” space if you should need to make your garment just a little bit looser.

When is the seam allowance not 5/8″ (1.5cm)?

To make your sewing easier on very small items such as doll clothes, on small detail pieces such as belt carriers and in larger areas where you would need to trim away the excess seam allowance, we typically reduce the seam allowance to 3/8″ or 1/4″(1.3cm or 6mm). But, as we said before, when the seam allowance is other than 5/8″ (1.5cm), the amount is specified both on the pattern piece and in the sewing instructions.

What if I need to make a smaller seam allowance?

On most fabrics, if we have indicated a 5/8″(1.5cm) seam allowance, you can stitch as much as 1/4″(6mm) closer to the cut edge and still have an adequate seam allowance. By doing this, you will make your garment a little bit bigger, either in circumference or length, depending on where the seams fall. CAUTION: If you are working on a fabric that ravels easily, it may not be wise to adjust to a smaller seam allowance, especially if the seam is in an area of high stress such as an armhole or fitted bodice side seam.

Remember that if you change the seam allowance in one place on the garment, you will have to do it on the corresponding sections. For example, if you change the side seam allowance at the underarm on a bodice, you will also have to change the underarm seam allowance on the sleeve or armhole facing.

Is the seam allowance ever more than 5/8″ (1.5cm)?

Occasionally there will be a specific reason for using a larger seam allowance, such as 3/4″ (2cm) or 1″ (2.5cm). One example is on a garment with a very fitted bodice where, because of its close-to-the-body fit, special adjustments may be necessary. We will always tell you when we have done this on a pattern.

Do I have to follow the seam line exactly?

When you’re starting out don’t worry if your stitches are a little wobbly or wavy. But as you go on you’ll find that you’ll achieve a more professional look to your garment, if your are stitches . If your seam lines are uneven, your garment might not hang quite right and you might experience fitting issues. If you have trouble keeping your stitching straight, use the guidelines on your presser foot or throat plate to help you. (If you’re not familiar with this feature, check your sewing machine’s manual.) You might even want to practice sewing on scraps of fabric or on a piece of typing paper. (For the latter, you don’t even need to thread your machine. The needles holes in the paper will tell you how well you are doing!)

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