How-to: Blend Between Sizes on Sewing Patterns

So, you’ve measured yourself, looked at the pattern sizing chart, and decided that you’ll need to blend between sizes. But how do you do it?

Blending between sizes is a useful technique for people that don’t fall into a standard size ratio that you’ll see on a pattern envelope/size chart. Perhaps your bust is smaller than average for your size, or maybe your hips are larger than the average for that size.

This is where blending comes in. It allows you to make minor alternations to your pattern pieces to ensure a good a good fit.

However, you won’t always need to blend between sizes. When checking out your measurements on the pattern envelope/size chart, also make sure to look at the finished garment measurements, and note the amount of ease. If the garment is intended to be more loose fitting, like a smock for example, you may not need to blend unless you’re 2-3 sizes different from the standard ratio. You can get away without blending on looser fitting items. However, I would recommend blending if the pattern is fairly fitted, like trousers/pants, a fitted dress or tailored shirt.

Ok, great, how do I blend?

First of all, identify the notches on your pattern pieces for the bust, waist and hips. If these aren’t marked on the pattern pieces, you can hold the piece up to your body, and mark where these places fall for you.

Alternatively, you’ll probably be able to tell just from looking at the pieces. For example, the waist is likely to be the narrowest point of the pattern piece, whilst the hip is likely to be the largest.

Next, take a pencil and draw a diagonal line from one notch to the next, blending the piece larger or smaller as necessary. Don’t forget to make the same adjustment to back pieces and any other corresponding pieces.

If the pattern piece is curved, you’ll want to use a French Curve Ruler to follow that curve when drawing in your new line so that you don’t alter the shape of the pattern.

For example:

I recently made the Tilly and the Buttons Indigo dress. My measurements didn’t fall into one single size, and my bust was 3 sizes smaller than my waist and hips.

So I decided to make the Size 9 waist and hips and blend to a Size 6 bust. This meant me using the bust notch and waist notch, drawing a diagonal line from the 6 line to the 9 line at the side seam, leaving all other lines in tact as a 6. Because these were left as a 6, the facings did not need altering.

I cut the arms as a size 6 also, so that they slotted into the size 6 bodice top, but used a smaller seam allowance to make them slightly bigger and be more comfortable on my arms.

Now that the waist was a size 9 meant cutting the skirt pieces as a size 9 to match.

In the end, the dress was too big at the waist (I could have used Size 8 or maybe even 7), but because of blending, it fits very well in the bust. I’ll just need to buy a belt to wear with it…

But…this is why we make toiles/muslins from cheaper fabric. I know next time I make this pattern that there is more ease than expected (despite finished measurements) and I could easily get away with making a smaller waist/hip size.


  • How to Blend Between Sizes – Seamwork:
  • How to Blend Between Sizes -Amy Nicole Studio:

Good luck!

Check back soon for more tips and tricks on pattern adjustments and fitting guides.

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