How to Trim and Grade Seams

Often in sewing the most basic techniques, such as how to trim and grade seams, are the most important. The first time I ever sat down at a sewing machine Angela taught me to strive for a professional finish. In other words to create a garment where the construction and finish is as good as a well made shop bought item. If you can achieve it the chances are you will feel even happier with your latest make and will want to wear it even more. To create the sought after 'professional finish' you will need to use a number of the basic techniques I refer to, including trimming and grading seams. In this article we share our top tips for how to trim and grade like a pro.

Why Trim And Grade Seam Allowances?

You can sew a lovely neat seam and press it perfectly, but if you don't trim and grade those seams where necessary you will be left with a bulky, bumpy appearance on the right side of the garment. Trimming refers to reducing a seam allowance to prevent bulk. Grading is used in an enclosed seam to reduce the bulk created by the layered seam allowances. Trim, grade and press in the right places and your seams will look as smooth as silk.

As always each garment and fabric is different and therefore these are general principles rather than hard and fast rules. Our mantra is always to test out on scraps first if you need a confidence boost before cutting into your actual garment. Over time your confidence will grow and you will probably find yourself improvising beyond these principles to find the best approach for new and different scenarios.


First things first not all seams need trimming. It depends on the location of the seam in the garment and the type of fabric. Side seams, centre back seams, panel seams and sleeve seams often won't need trimming. Once they are finished and pressed open they will sit smoothly with no bulk or ridges. However, if you are working with an extremely bulky non fraying fabric you may wish to trim every seam.

On the other hand seams on collars, lapels, facings and underarms always need trimming regardless of the fabric. Trimming curved underarm and crotch seams can help to make these garments more comfortable to wear. The acid test is to consider whether the seam will be bulky or uncomfortable if you don't trim it down. Although it is also important to consider whether a seam will be under a lot of strain. If so you may need to reinforce the seam before trimming to avoid an embarrassing wardrobe malfunction! I'm thinking crotch seams here people!

Trimming may also be necessary where seams intersect. For example, on a skirt where the vertical side seam crosses the horizontal waistband seam. There are two options here:

Option One

Diagonally trim the ends of the top seam before sewing the intersecting seam. This way you can trim beneath the intersecting seam line as well as above. If you sew the intersecting seam first you will only be able to trim diagonally above the intersecting seam line. I have used contrasting threads and fabrics in the images below so they are easy to interpret.

Trimming Intersecting Seams

Option Two

Trim the corners down close to the seam, about 1/8" to 1/16" depending on how bulky the fabric is. I tucked the ends of my overlocker thread under the overlocking stitches on the right side of the fabric here, but you could do it on the wrong side for a neater finish if the seam allowances will be visible.

Trimming Seams That Intersect

When using bulky fabrics you may also wish to trim the seam allowances of hems and facings. This is because the seams become layered - when you press the hem up it layers over the side seam, for example. Here you can simply trim the seam allowances within the hem allowance or facing. If the fabric is especially bulky you can also take small notches out of the hem allowance at the hemline.

Trimming Hem Seam Allowances

Always remember to test the fit of your garment before trimming. A good general rule of thumb is to trim seams to 1/4" unless working with a loosely woven fabric, in which case trim to around 3/8". If working with a fabric that frays easily trim, finish then press the seam. In these cases, if finishing the seam with an overlocker or overcasting stitch, it may be easier to finish the seams together rather than separately because you are working with less fabric. We always recommend finishing seams before pressing. If you press then finish you are lifting up the seam allowances you have just pressed down. We wrote a blog article with all our top tips for pressing here.

Trimming Darts

When working with heavier fabrics you can also reduce the bulk created by any darts. If the top of the dart is 1/2" to 5/8" wide cut along the fold stopping 1/4" before the point. Clip the seam allowance on one side towards the dart stitching line and this will allow you to press the dart open and press the small section at the bottom to one side. If a dart is wider than 5/8" trim it down to 5/8" first and repeat the steps above.

Trimming Darts


Grading is mostly used in enclosed seams such as collars, lapels and cuffs. However, I always grade the waistband seams on a skirt, which isn't an enclosed seam in the same sense. The waistline is definitely somewhere I want to reduce bulk though! There may be other areas where you decide grading is a sensible move depending on the fabric and the garment.

Grading seams is trimming the seam allowances to different widths. Start with the seam allowance that will sit furthest away from the right side of the garment. This will be the seam allowance you will trim down the most, usually to about 1/8". Move onto the next seam allowance and trim it to 1/4" i.e. 1/8" wider than your last one. If there are further seam allowances continue to trim 1/8" wider than the last. The widest seam allowance should always be the one that sits closest to the right side of your garment. This is because it will hide the staggered seam allowances you created underneath.

Grading Seam Allowances

You can even use your overlocker to finish and grade seams at the same time by increasing/decreasing the amount you shave off each seam allowance. Whether or not you finish the seam allowances is down to personal preference, fabric type and the location in the garment. For example, if the fabric frays easily it is best to finish the seam allowances. However, if it is a lined garment and the seam allowances will not be visible you may choose not to finish them.

If working on a garment with front facings and lapels the right side of the fabric switches where the lapels fold over. I.e the side that was on the wrong side of the garment flips over to become the right side of the garment where the lapel folds over. Therefore you will need to switch your grading order at this point too. Just remember to make sure the widest seam allowance is next to whichever the right side of the fabric is at that point. You will also need to clip where the lapel folds back to allow it to roll over.

For curved seams such as princess seams I always grade first then clip or notch to get a neat finish.

Grading Princess Seams

Always take great care when grading seams remembering it is possible to accidentally snip the main garment fabric. Yes, I've definitely done it and felt my heart sink into my shoes as the realisation hit home. One thing that will help you to avoid this scenario is a good pair of small scissors such as my Janome embroidery scissors in the image above. It is much easier to make smaller, controlled movements with these than a standard sized pair of scissors. You can find our full range of scissors here and if you ever need any advice don't hesitate to contact us.

That's all for this week folks!

Have fun sewing!


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