Back to Basics: What is a Seam Allowance

Whatever you're creating when sewing, there's one thing that you create no matter what and that's a seam allowance. Take a look at your shirt, your drapes, or even your shoes and you'll find seams everywhere!

What’s a Seam?

Making a seam means to bind or sew two things together. A seam in sewing is the line where two pieces of fabric are joined together with stitching. You could sew right down the middle of a piece of fabric and that would be a seam. Though a seam is usually sewn close to the edge of the fabric. 

Floral fabric folded with right sides together

When you sew a seam you usually place your two pieces of fabric with the right sides together. That way your seam is hidden from the right side of the fabric. Check out the GIF below to see what I mean:

Animated gif of floral fabric folded and opened.

See how sewing on the “wrong side” (the back side) of the fabric keeps the seam allowance from being visible from the front? Pretty smart eh.

Image with four pictures of sewing activities and the words What is a seam allowance? Back to Basics with

What’s the Seam Allowance?

A seam allowance is the width of fabric from your seam stitches to the edge of the fabric. This is the width of fabric that will be hidden inside.

Seam allowances range in all different widths, from 1/4” to 1” or more! If you’re working with a pattern it will usually tell you how wide to make your seam allowance. Some patterns don’t include any seam allowance, in which case you will be adding some to your pattern pieces. More on that later… 

It is important to try and be accurate and consistent with your seam allowance. If you are making clothing this is especially important as just 1/8 of an inch off can make your garment an entirely different size.

If you’re planning on making something without using a pattern and you don’t know how much of a seam allowance to figure in then you can use this guide.

Determining the Best Seam Allowance For Your Project

  • Is the seam on a curve?  1/4” seam allowance is best for curves because there’s less bulk and your curve will look smoother. If you are sewing a wider seam allowance on a curve, you can also trim your seam allowance down to a 1/4” after it’s sewn. It’s easier to sew curved seams with a smaller seam allowance more accurately. 
  • Will I be adjusting the fit? If you’re sewing something that needs to be fitted to your body you might want to leave a 5/8”+ seam allowance. This allows you to “let the seam out” if you need to, making the garment bigger if need be. 
  • Will I be serging my seam? If you’ll be overlocking or serging your seam then you should use a 3/8” or 1/2” seam allowance depending on how wide of an overlock you will use. This gives your serger a little bit to cut off of the seam while you serge it. 
  • Making a french or flat felled seam? To make a French seam or a flat felled seam you’ll need to have 5/8” seam allowances. 
  • What’s a good middle standard? You can use a 1/2″ or 3/8″ seam allowance. I prefer 3/8” as it makes sewing curves easier and is the perfect amount for overlocking the seam. The standard seam allowance in most DIBY Club patterns is 3/8” for knit patterns and 5/8″ for woven patterns (these are typical universal standards).

Adding Seam Allowance to a Pattern

If you are drafting your own pattern or your pattern does not have a seam allowance included, you can easily and quickly add one.

Paper sewing pattern piece with no seam allowance with a pencil and a rule

First trace your pattern onto a piece of paper and give yourself room to add to it. I’ll share my best kept secret when it comes to making my own patterns. Go to Hobby Lobby and when you check out, ask if you can have some of the paper that they use to wrap breakables. I think it’s the best pattern paper! It’s thin and can be seen through if your tracing, it’s large, and it’s free!

Picture of paper pattern piece with woman's hand adding seam allowance with a protractor

Now, I’m sure you haven’t seen a protractor since you were in high school but you can probably get one at Hobby Lobby! It makes adding a seam allowance a breeze. Just open it to the width of the seam allowance you’re wanting to add and trace around your pattern!

A couple things to note. Don’t add any seam allowance to sides that will be placed on the fold. Also you will likely need to add more hem allowance than you have for your seams. You’ll also need to add more of a seam allowance for zipper or button seams, or if you plan on sewing a French or flat felled seam.

Paper pattern piece with seam allowance drawn on with protractor, ruler, and pencil on top of paper

Your pattern may end up have a couple different seam allowances and that’s perfectly ok! I like to mark my patterns so that when I use them in the future I know exactly what seam allowance I have to sew.

Sewing the Correct Seam Allowance

To make a seam with the proper seam allowance we’ll need to first determine where that seam allowance is on your machine. Most sewing machines will have a ruler engraved into the needle plate. (Not sure what a needle plate is? You’ll love learning all that sewing terminology in our article about how to use a sewing machine.)

Sewing machine sewing a seam on a piece of floral fabric with wrong side up

If your machine’s needle can be moved into multiple different positions, however, the seam guide printed on your needle plate will become inaccurate as it is based on the needle being in a specific position.

My machine’s seam guide is only accurate if my needle is in the far left position. I can then line up the edge of my fabric with the seam allowance marking that I want. Your machine will be different so you’ll want to measure from your needle to your seam guide to find out.

Picture of measuring tape being used to measure seam lines of a sewing machine

 But If I want to use the edge of my pressure foot as a guide and I want a 1/4” seam allowance, I can also just simply adjust my needle to the right position. I again use my sewing tape to measure this so that I get an accurate seam allowance. 

Measuring tape on a piece of floral fabric measuring seam allowance

Removing a Seam

And finally when sewing seams you’re going to make mistakes and that’s ok! We all do it no matter how experienced we are. Luckily we have this handy dandy tool called the seam ripper. This little guy will become your new best friend. It’ll make easy work of taking those seam stitches out. I probably have four seam rippers in my sewing room because I absolutely cannot live without them!

Simply slide it under a stitch until it cuts it and repeat about every 5 stitches down the length of seam that you want to remove. Check out how easy it is to sew over a section of stitches that you ripped out.

Picture of wrong side of floral fabric with blue stitches and pink seam ripper

Now that you’ve learned all about seams and seam allowances you’re ready to learn how to finish you seams. There are many ways to finish a seam and it’s the number one thing that can either make your clothes look homemade or like it was manufactured. Head on over there now!


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