Arune Guja

What is Seam Allowance?

Are you new to sewing? One of the first things you will encounter when learning sewing basics will be a thing called seam allowance. What is seam allowance? How to add seam allowance and how to determine which seam allowance to use? Here are the answers to all of these questions.

What is seam allowance?

What is seam allowance? Seam allowance is the area between the raw edge of the fabric and the stitching line (seam line). In other words, seam allowance is a space from the edge of the garment panel to the seam itself. 

Seam allowance mainly serves a safety purpose - it prevents the stitching of the seam from being too close to the edge, thus allowing two fabric pieces to be connected in a reliable way. 

Another purpose of a seam allowances (especially big ones) is that it allows the garment piece to be altered in the future. Leaving a wide seam allowance on custom fitted garments allows the seam to be ‘’let out’’ if the garment is too tight. Leaving a wider seam allowance on the hem of the garment allows it to be lengthened in the future.

Why is seam allowance important?

Seam allowance is an important aspect when trying to assemble the garment. When sewn incorrectly it can change the size and the fit of the garment. Too small seam allowance can shorten the lifespan of the garment by allowing the fabric around the seam to be torn. In other words too small seam allowance can contribute to seam slippage. Too big seam allowance can add bulkiness to the seams and contribute to the unprofessional look of the seam finish.

What are standard seam allowance options?

There are few standard seam allowance options: 

1/4" (inches) - 0,6 centimeter

 3/8" (inches) - 1 centimeter

1/2" (inches) - 1,3 centimeter

5/8" (inches) - 1,5 centimeter

3/4" (inches) - 2 centimeter

1" (inches) - 2,5 centimeter

Each sewing project may require a different seam allowance. Seam allowance used may also vary from one pattern designer to another, and also it may differ from one country to another. Most commonly used in the USA is the 5/8" (1,5 cm) seam allowance option and in other parts of the world the most common is the 3/8’’ (1 cm ) seam allowance. Good thing is, if you have a pattern on which the seam allowance is not included - you can decide which one you want to add.

How to determine which seam allowance option to use?

There are couple of rules for using different types of seam allowances:

  • When the seam is curved it is always better to use a smaller seam allowance - 1/4"(0,6cm). It will prevent the excess fabric and will allow your seam to look less bulky. When using a small seam allowance you won't need to trim the seam allowance afterwards. 
  • 1/4"(0,6cm) seam allowance is also recommended for quilting projects. This size seam allowance does not create bulky seam, but at the same time leaves enough space when piecing the panels together.
  •  If you are planning to adjust the garment fit or length in the future - use wider seam allowance, like 5/8"(1,5cm), 3/4"(2cm) or 1"(2,5cm). By doing that you will have some extra fabric space to work with. These are great options when adding hem allowance.
  • When making French seam or flat felled seam use 5/8"(1,5cm) seam allowance.
  • When serging your seams use middle options like 3/8"(1cm) or 1/2"(1,3cm).
  • If you want a good middle option use 3/8"(1cm) for knit patterns and  5/8"(1,5cm) for woven patterns. It will give an optimal outcome to all of your seams.

When to trim seam allowance?

Trimming seam allowance prevents excess fabric creating bulky seam and distorting the look of it. It is recommended around curved areas, like the armhole, neckline, and curved hem. You can also do that for curved seams like princess seams or round shaped garment panels like pockets. It also works great when working with interfacing, underlining or interlining. Working with multiple layers of fabric can also add bulkiness to the seams. Therefore trimming seam allowance of inner layers is also recommended. 

To trim the seam allowance for straight seams you have to actually make it smaller.  For trimming curved seams, you can either cut out multiple tiny triangles with the top facing the stitching line or make multiple tiny cuts, thus allowing it to be shaped easily.

When to add a bigger seam allowance?

Add a bigger seam allowance when you know that you will adjust the size or the length of the garment. You can always leave a bigger seam allowance on the hems to keep the garment flexible for length adjustments. It is also wise to add a larger seam allowance when working with fabric that fray easily to prevent seam slippage.

What is a seam guide?

Seam guide is a small metal sewing tool attached next to the presser foot. Seam guides are usually magnetic and are attached to the metal stitch plate of the sewing machine. The tool acts as a wall that does not allow fabric to change it’s distance, thus helping you keep a consistent size seam allowance and a straight stitching line. This tool works great if you have decided upon a seam allowance and want to keep it precise. Sewing with this tiny magical tool can save you some time and make you forget about your seam ripper. 

Do patterns include seam allowance?

In pattern making, a sewing pattern is drafted without seam allowance and it is added as the last step. In most cases it is added already on the actual fabric, not on the pattern itself. When buying a sewing pattern, seam allowance is included in some commercial patterns but not all. It again depends on a pattern designer, brand and also the country. European patterns less likely will include the seam allowance, than the ones made by USA companies. Adding seam allowance yourself is a task, but it allows you to choose which one you want to use. Some creators prefer smaller seam allowance and some like to use larger seam allowance. On the opposite side of the spectrum, removing a seam allowance that is already added can be a hassle.

How to add seam allowance to your pattern?

To add seam allowance to your sewing pattern, place the pattern pieces on the fabric with enough space between them.

Take your tailor's chalk or pencil and a ruler and trace it all around the pattern while constantly measuring the distance from the edge of the sewing pattern. Add other pattern markings if needed. Take scissors and cut out the panels including seam allowance. Don’t forget to make tiny cuts or cut out tiny triangles for notches.

Do not add the seam allowance to the edge of the pattern that needs to be cut on the fold.

If you want to read more about how to add seam allowance to your sewing pattern check out this article HOW TO ADD SEAM ALLOWANCE TO A PATTERN

Jul 25, 2021