Thursday Tip // Seam Allowance

When you learn something new, whether it’s a new skill, a new job, a new recipe; you will undoubtedly come across new terms and concepts that you’ve never seen before or may have heard of before but never really understood. Learning to sew is no different!

There’s tons of new vocabulary to learn and that’s why we are here. We really hope this series of beginner tips give you beginner sewists some confidence to start your first project or keep plugging away at that new thing you are tackling. This week we discuss the term “seam allowance” and why it is important for sewing success!

What is seam allowance?

When you sew two fabrics together to create a seam you need to leave a bit of space between the raw edge and the stitching line where you are sewing. This space is called the seam allowance. Seam allowances can range from ¼ inch wide to several inches wide depending on the project, type of fabric and type of seam finish you are using. Commercial (home) sewing patterns typically have seam allowances between ¼ inch to ⅝ inch.

Why is a seam allowance important?

Without a seam allowance sewing two layers of fabric together right at the raw edges can be next to impossible. The fabric pieces may not be lined up exactly or be cut exactly the same so stitching right on the edge can cause you to miss a layer of fabric and have holes in your seam. 

If your fabric frays really easily a stitching line right on the raw edge can just fray right off when the fabric is handled.

It is always necessary to sew with a seam allowance so you catch all layers of fabric in the seam, the seam stays secure for a long time and you can properly finish the raw edges of the fabric without interfering with the stitching line.

The main goal for seam allowances is accuracy. Keeping a straight and accurate seam allowance is important in order to achieve the desired fit of the garment. Consider a woven top for example. If the seam allowance is supposed to be ½ inch and you sew the side seams at 1 inch seam allowance you have now made the garment smaller by subtracting a total of 1 inch (½” on each side of the top) from the entire circumference of the top. If you now try to attach set-in sleeves, the arm hole has shrunk by ½” on each side as well and the sleeve won’t fit. 

Seam allowance and fitting the garment

A seam allowance also gives the garment some wiggle room when it comes to alterations. If you sew a pair of pants with a ⅝ inch seam allowance and you find they are a little too tight across the thighs then you can unpick and sew the outer leg seams again with a slightly smaller seam allowance (eg. ⅜ inch) and give yourself that room to sit down and bend at the knees properly without major changes to your garment. With ample seam allowance you can make changes to garments later on as well which is great because our bodies fluctuate all the time and this way our clothes can too!

A seam allowance will always be necessary when sewing anything from garments to quilts to stuffed animals to pillow covers, you name it, it’ll have a seam allowance. Garments will typically have seam allowances in the range of ⅜” - ⅝” with knit garments tending to have smaller seam allowances between ¼”-⅜”. 

Where do I find the seam allowance?

Seam allowance is generally included in the pattern pieces on most indie patterns but it is always a good idea to check before cutting your fabric. If seam allowances are not included you will need to add the seam allowance to your pattern pieces or directly on your fabric when you cut the pieces out.

The pattern instructions should include the seam allowance for the garment. It will say something like “seam allowances are ⅝” unless otherwise stated” so you can assume it is ⅝” throughout all parts of construction except when the instructions indicate a different seam allowance. Seam allowances can sometimes differ depending on the part of the garment you are constructing or what type of seam finish is suggested. Hem allowances are often larger than construction seam allowances so just watch out for those instructions.

Sewing with a seam allowance

When sewing you can find the seam allowance markings on the needle plate of your sewing machine. These markings will vary depending on the type of sewing machine. If the markings aren’t clear enough you can use a sewing gauge lined up with the needle to check your seam allowance and then mark it on the needle plate with painter’s tape, washi tape or a sticky note (something that won’t leave a residue). Sometimes this is helpful to do anyway so you can remember the seam allowance for a particular project you are working on. This will help you keep a straight and accurate seam allowance.

Note: You can also buy different types of magnetic seam gauges that help you keep your seams straight by attaching the guide to your needle plate. However, some machines don’t have a large enough needle plate to accommodate these types of guides so do a bit of research first. Also, if you have a computerized sewing machine be wary of using anything magnetic attached to the machine as it can mess with the computerized components of the machine.

Next week we will discuss several options for how to finish a seam and how seam allowances come into play there. Happy sewing!