The seam allowance of a sewing pattern is simply the extra room around the stitching lines and the raw edge. This lets you know how far in from the cut raw edge you will be sewing your seam.
What is seam allowance?
Seam allowance is a margin between the cut raw edge and the line along which you will be sewing along. It helps determine the final size and shape of the item and allow for fraying edges.
Why is it Important?
Using the wrong seam allowance will mean your clothing may be too big or too small so it is important to learn how to add seam allowance correctly and how to sew the correct sized seam.
Maintaining the seam allowance allows the fabric to fray without interfering with the integrity of the item. Seams may need to be clipped or pressed open for different purposed and the pattern designer will have factored this into their decisions.
Standard Seam Allowance
Unfortunately, there is no universally correct seam allowance.
It is important to note that different designers will have different rules so it is always important to check carefully before you start cutting. The seam allowance will always be specified in the pattern notes which are at the beginning of patterns.
The actual seam allowance will also vary depending on the project. Knit fabric patterns typically have smaller seam allowances than woven fabric projects. In addition, a small item such as a hair bow may have a smaller seam to reduce bulk.
Most designers keep the seam allowance consistent throughout the pattern but there may be times where it changes for a particular step. This will be clearly outlined in your pattern.
It is common for European designers to add NO seam allowance to their patterns and you need to manually add it in before sewing. In the how to add seam allowance section I will show you how to do this.
Burda Style Magazine patterns commonly DON"T have seam allowance added. Simplicity, New Look and Butterick generally DO have them added.
Treasurie and My Childhood Treasures Patterns
My patterns all include the seam allowance which means you don’t need to alter the pattern in any way. You just cut around the pattern and start sewing.
As a general rule, Treasurie and My Childhood Treasures’ (MCT) sewing patterns have the following seam allowance included.
(There are always some exceptions so please check your pattern before you start.)
- Wovens: ½ inch (12mm)
- Knits: ⅜ inch (1cm)
- Leotards: ¼ inch (12mm)
- Doll’s clothing: ¼ inch (6mm)
- Clutches/Bags: ⅜ inch (1cm)
HOW TO ADD SEAM ALLOWANCE
If you have a pattern from a designer that needs a seam allowance added here is what you do. You can add your seam allowance directly onto your fabric or onto paper first.
Regular Seams (Side seams and shoulders)
Use this method to add seams for armholes, shoulders and side seams. There is a different method for hems and placing on the fold and these will be discussed in the next sections.
Adding Seam Allowance to Seams
- Place Pattern on Paper
Place your pattern pieces on your fabric or paper with enough room between them to add the seam allowance. Decide what seam allowance you would like to add.
If you are a beginner and not sure what to add, then refer to my rules above.
- Mark the Seam Allowance
Using chalk or removable pen, add the seam allowance all around the pattern using your ruler.
If you have a regular ruler just make a series of dashes and join them up. It can be a bit faster if you use a quilting ruler as you can draw longer lines at once.
For curved parts, make a series of small dashes and join them up. You can use a curved ruler or French curve at the end to smooth out the curve.
- Seam Allowance on the Fold
Just to trick you up there are a couple of exceptions. Do not add seam allowance on a seam that is placed on the fold of the fabric.
How to Add Seam Allowance to Hems
Where you have a hem you may need to add extra seam allowance. Your pattern instructions should specify how much. If it doesn’t then try adding ¾ inch (2cm) any hems. This allows you to turn the hem twice. Once at ¼ inch (6mm) then again at ½ inch(12mm).
If you need to add seam allowance to an angled piece such as a sleeve, continuing at the same angle means the hem will become too narrow when folded. You will need to angle the hem outwards as shown in the diagram.
HOW TO ADD SEAM ALLOWANCE | Hacks
1. Marking Hack
Use this easy sewing hack. Add seam allowance by joining 2 pencils together with a rubber band.
Use one to mark and the other to guide around the edge.
2. Distance Hack
New sewers may want to put a piece of colored tape along the seam guide they will be using. You can use painters tape if you are worried about it marking your machine.
I've seen some people recommend using rubber bands to mark the distance but in my experience, the rubber bands move around meaning you may lose accuracy. A piece of tape is not going anywhere!
STITCHING THE CORRECT SEAM ALLOWANCE
Once you have cut your fabric out you will need to stitch it together using the correct seam allowance.
If you look at the plate of your sewing machine you will see that there are different numbers and lines marked. These are the seam guides.
When the needle is in its center position you should align the raw edges of your fabric with the appropriate seam allowance guide. Start stitching maintaining the same distance.
Now that you are ready to sew, I have an entire article on how to sew a seam. This will show you the correct position and settings and a few tricks and tips on sewing a perfectly straight seam.
Now you have added the seam allowance, the next step is to start cutting your fabric. Here is an article showing you which direction to place the pattern and tricks like cutting on the fold.